Apolipoprotein(a) Genetic Sequence Variants Associated With Systemic Atherosclerosis and Coronary Atherosclerotic Burden But Not With Venous Thromboembolism

The Association of SNPs Located in the CDKN2B-AS1 and LPA Genes With Carotid Artery Stenosis and Atherogenic Stroke

Introduction: The aim of this project was to assess the prevalence of four selected SNPs rs4977574 and rs7857345 (CDKN2B-AS1 gene) and rs3798220 and rs10455872 polymorphisms (the LPA gene) in the subpopulation of patients with symptomatic and asymptomatic carotid stenosis.

Material and Methods: This study included 623 individuals (244 patients with symptomatic carotid artery stenosis, 176 patients with asymptomatic carotid artery stenosis and 203 healthy people. All the participants underwent neurological examination, duplex Doppler ultrasound examination and molecular procedures.

Results: In the first part of the analysis the assiociation of SNPs with stroke/TIA was investigated. The association was seen in symptomatic vs. control group for two SNPs: rs4977574 and rs7857345 (CDKN2B-AS1 gene); genotype distributions for rs4977574 and rs7857345 showed the statistically significant differences between patients and controls (p = 0.043 and 0.017, respectively). No association was observed for rs3798220 and rs10455872 located in the LPA gene. There were statistically significant differences between asymptomatic patients vs. control group in genotype distribution for the SNPs located in CDKN2B-AS1: rs4977574 and rs7857345 (p = 0.031 and 0.0099, respectively); and for the rs3798220 (LPA gene; p = 0.003); however, statistically significant differences did not occur for the rs10455872 polymorphism located in the LPA gene. In the next part of the evaluation, a comparison between symptomatic and asymptomatic patients was performed. Significant differences in genotype distribution were seen only for the rs3798220 polymorphism located in the LPA gene (p = 0.0015). The analysis of the prevalence of the polymorphisms in the total group (symptomatic and asymptomatic) patients in comparison with the control group showed significant differences for three polymorphisms: rs4977574 and rs7857345 (CDKN2B-AS1 gene; p = 0.015 and 0.0046, respectively) and rs3798220 (LPA gene, p = 0.044).

Conclusions: The present research on the carotid artery stenosis patient cohort suggests the significant association between the rs4977574, rs7857345 and rs3798220 polymorphisms and carotid artery stenosis as well as between the rs4977574 and rs7857345 polymorphisms and atherogenic stroke. The rs4977574 and rs7857345 polymorphisms in patients with carotid artery stenosis appear to affect a person's susceptibility to atherogenic brain ischemia. Our results need to be replicated in future studies.

Causal Effect of Lp(a) [Lipoprotein(a)] Level on Ischemic Stroke and Alzheimer Disease: A Mendelian Randomization Study

Background and Purpose- Stroke and Alzheimer disease are 2 major causes of neurological disability in aged people and shared overlapping predictors. In recent prospective studies, high Lp(a) [lipoprotein(a)] level is associated with high risk of stroke but low risk of Alzheimer disease. Whether this reflects a causal association remains to be established. The aim of this study is to examine the causal associations of Lp(a) concentrations on ischemic stroke, ischemic stroke subtypes, and Alzheimer disease. Methods- We used 9 single-nucleotide polymorphisms associated with Lp(a) concentrations as instrumental variables. Summary-level data on ischemic stroke and its subtypes were obtained from the Multiancestry Genome-Wide Association Study of Stroke consortium with European individuals ≤446 696 individuals. Summary-level data on Alzheimer disease were obtained from the International Genomics of Alzheimer Project With European individuals ≤54 162 individuals. Two-sample Mendelian randomization (MR) estimates were calculated with inverse-variance weighted, penalized inverse-variance weighted, simple median, weighted median, and MR Pleiotropy Residual Sum and Outlier approaches, and MR-Egger regression was used to explore pleiotropy. Results- Genetically predicted 1-SD log-transformed increase in Lp(a) concentrations was associated with a substantial increase in risk of large artery stroke (odds ratio, 1.20; 95% CI, 1.11-1.30; P<0.001) and a reduce in risk of small vessel stroke (odds ratio, 0.92; 95% CI, 0.88-0.97; P=0.001) and Alzheimer disease (odds ratio, 0.94; 95% CI, 0.91-0.97; P<0.001) using inverse-variance weighted method. No significant association was observed for total ischemic stroke or cardioembolic stroke. MR-Egger indicated no evidence of pleiotropic bias. Results were broadly consistent in sensitivity analyses using penalized inverse-variance weighted, simple median, weighted median, and MR Pleiotropy Residual Sum and Outlier approaches accounting for potential genetic pleiotropy or outliers. Conclusions- This study provides evidence to support that high Lp(a) concentrations was causally associated with an increased risk of large artery stroke but a decreased risk of small vessel stroke and Alzheimer disease. The mechanism underlying the double-edged sword effect of Lp(a) concentrations on neurological system requires further investigation.

Potent reduction of plasma lipoprotein (a) with an antisense oligonucleotide in human subjects does not affect ex vivo fibrinolysis

It is postulated that lipoprotein (a) [Lp(a)] inhibits fibrinolysis, but this hypothesis has not been tested in humans due to the lack of specific Lp(a) lowering agents. Patients with elevated Lp(a) were randomized to antisense oligonucleotide [IONIS-APO(a)_Rx] directed to apo(a) (n = 7) or placebo (n = 10). Ex vivo plasma lysis times and antigen concentrations of plasminogen, factor XI, plasminogen activator inhibitor 1, thrombin activatable fibrinolysis inhibitor, and fibrinogen at baseline, day 85/92/99 (peak drug effect), and day 190 (3 months off drug) were measured. The mean ± SD baseline Lp(a) levels were 477.3 ± 55.9 nmol/l in IONIS-APO(a)_Rx and 362.1 ± 89.9 nmol/l in placebo. The mean± SD percentage change in Lp(a) for IONIS-APO(a)_Rx was -69.3 ± 12.2% versus -5.4 ± 6.9% placebo (P < 0.0010) at day 85/92/99 and -15.6 ± 8.9% versus 3.2 ± 12.2% (P = 0.003) at day 190. Clot lysis times and coagulation/fibrinolysis-related biomarkers showed no significant differences between IONIS-APO(a)_Rx and placebo at all time points. Clot lysis times were not affected by exogenously added Lp(a) at concentrations up to 200 nmol/l to plasma with very low (12.5 nmol/l) Lp(a) levels, whereas recombinant apo(a) had a potent antifibrinolytic effect. In conclusion, potent reductions of Lp(a) in patients with highly elevated Lp(a) levels do not affect ex vivo measures of fibrinolysis; the relevance of any putative antifibrinolytic effects of Lp(a) in vivo needs further study.

Novel Drug Targets for Ischemic Stroke Identified Through Mendelian Randomization Analysis of the Blood Proteome

BACKGROUND

Novel, effective, and safe drugs are warranted for treatment of ischemic stroke. Circulating protein biomarkers with causal genetic evidence represent promising drug targets, but no systematic screen of the proteome has been performed.

METHODS

First, using Mendelian randomization (MR) analyses, we assessed 653 circulating proteins as possible causal mediators for 3 different subtypes of ischemic stroke: large artery atherosclerosis, cardioembolic stroke, and small artery occlusion. Second, we used MR to assess whether identified biomarkers also affect risk for intracranial bleeding, specifically intracerebral and subarachnoid hemorrhages. Third, we expanded this analysis to 679 diseases to test a broad spectrum of side effects associated with hypothetical therapeutic agents for ischemic stroke that target the identified biomarkers. For all MR analyses, summary-level data from genome-wide association studies (GWAS) were used to ascertain genetic effects on circulating biomarker levels versus disease risk. Biomarker effects were derived by meta-analysis of 5 GWAS (N≤20 509). Disease effects were derived from large GWAS analyses, including MEGASTROKE (N≤322 150) and UK Biobank (N≤408 961) studies.

RESULTS

Several biomarkers emerged as causal mediators for ischemic stroke. Causal mediators for cardioembolic stroke included histo-blood group ABO system transferase, coagulation factor XI, scavenger receptor class A5 (SCARA5), and tumor necrosis factor-like weak inducer of apoptosis (TNFSF12). Causal mediators for large artery atherosclerosis included ABO, cluster of differentiation 40, apolipoprotein(a), and matrix metalloproteinase-12. SCARA5 (odds ratio [OR]=0.78; 95% CI, 0.70-0.88; P=1.46×10^-5) and TNFSF12 (OR=0.86; 95% CI, 0.81-0.91; P=7.69×10^-7) represent novel protective mediators of cardioembolic stroke. TNFSF12 also increased the risk of subarachnoid (OR=1.53; 95% CI, 1.31-1.78; P=3.32×10^-8) and intracerebral (OR=1.34; 95% CI, 1.14-1.58; P=4.05×10^-4) hemorrhages, whereas SCARA5 decreased the risk of subarachnoid hemorrhage (OR=0.61; 95% CI, 0.47-0.81; P=5.20×10^-4). Multiple side effects beyond stroke were identified for 6 of 7 biomarkers, most (75%) of which were beneficial. No adverse side effects were found for coagulation factor XI, apolipoprotein(a), and SCARA5.

CONCLUSIONS

Through a systematic MR screen of the circulating proteome, causal roles for 5 established and 2 novel biomarkers for ischemic stroke were identified. Side-effect profiles were characterized to help inform drug target prioritization. In particular, SCARA5 represents a promising target for treatment of cardioembolic stroke, with no predicted adverse side effects.

Nucleic Acid Therapies for Ischemic Stroke

Stroke remains a leading cause of disability and death worldwide despite significant scientific and therapeutic advances. Therefore, there is a critical need to improve stroke prevention and treatment. In this review, we describe several examples that leverage nucleic acid therapeutics to improve stroke care through prevention, acute treatment, and recovery. Aptamer systems are under development to increase the safety and efficacy of antithrombotic and thrombolytic treatment, which represent the mainstay of medical stroke therapy. Antisense oligonucleotide therapy has shown some promise in treating stroke causes that are genetically determined and resistant to classic prevention approaches such as elevated lipoprotein (a) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Targeting microRNAs may be attractive because they regulate factors involved in neuronal cell death and reperfusion-associated injury, as well as neurorestorative pathways. Lastly, microRNAs may aid reliable etiologic classification of stroke subtypes, which is important for effective secondary stroke prevention.

Lipoprotein(a): An independent, genetic, and causal factor for cardiovascular disease and acute myocardial infarction

Lipoprotein(a) [Lp(a)] is a circulating lipoprotein, and its level is largely determined by variation in the Lp(a) gene (LPA) locus encoding apo(a). Genetic variation in the LPA gene that increases Lp(a) level also increases coronary artery disease (CAD) risk, suggesting that Lp(a) is a causal factor for CAD risk. Lp(a) is the preferential lipoprotein carrier for oxidized phospholipids (OxPL), a proatherogenic and proinflammatory biomarker. Lp(a) adversely affects endothelial function, inflammation, oxidative stress, fibrinolysis, and plaque stability, leading to accelerated atherothrombosis and premature CAD. The INTER-HEART Study has established the usefulness of Lp(a) in assessing the risk of acute myocardial infarction in ethnically diverse populations with South Asians having the highest risk and population attributable risk. The 2018 Cholesterol Clinical Practice Guideline have recognized elevated Lp(a) as an atherosclerotic cardiovascular disease risk enhancer for initiating or intensifying statin therapy.

New Frontiers in Lp(a)-Targeted Therapies

Interest in lipoprotein (a) [Lp(a)] has exploded over the past decade with the emergence of genetic and epidemiological studies pinpointing elevated levels of this unique lipoprotein as a causal risk factor for atherosclerotic cardiovascular disease (ASCVD) and calcific aortic valve disease (CAVD). This review summarizes the most recent discoveries regarding therapeutic approaches to lower Lp(a) and presents these findings in the context of an emerging, although far from complete, understanding of the biosynthesis and catabolism of Lp(a). Application of Lp(a)-specific lowering agents to outcome trials will be the key to opening this new frontier in the battle against CVD.

Dietary natural products as emerging lipoprotein(a)-lowering agents

Elevated plasma lipoprotein(a) (Lp(a)) levels are associated with an increased risk of cardiovascular disease (CVD). Hitherto, niacin has been the drug of choice to reduce elevated Lp(a) levels in hyperlipidemic patients but its efficacy in reducing CVD outcomes has been seriously questioned by recent clinical trials. Additional drugs may reduce to some extent plasma Lp(a) levels but the lack of a specific therapeutic indication for Lp(a)-lowering limits profoundly reduce their use. An attractive therapeutic option is natural products. In several preclinical and clinical studies as well as meta-analyses, natural products, including l-carnitine, coenzyme Q ₁₀ , and xuezhikang were shown to significantly decrease Lp(a) levels in patients with Lp(a) hyperlipoproteinemia. Other natural products, such as pectin, Ginkgo biloba, flaxseed, red wine, resveratrol and curcuminoids can also reduce elevated Lp(a) concentrations but to a lesser degree. In conclusion, aforementioned natural products may represent promising therapeutic agents for Lp(a) lowering.

Rare thrombophilic conditions

Thrombophilia, either acquired or inherited, can be defined as a predisposition to developing thromboembolic complications. Since the discovery of antithrombin deficiency in the 1965, many other conditions have been described so far, which have then allowed to currently detect an inherited or acquired predisposition in approximately 60-70% of patients with thromboembolic disorders. These prothrombotic risk factors mainly include qualitative or quantitative defects of endogenous coagulation factor inhibitors, increased concentration or function of clotting proteins, defects in the fibrinolytic system, impaired platelet function, and hyperhomocysteinemia. In this review article, we aim to provide an overview on epidemiologic, clinic and laboratory aspects of both acquired and inherited rare thrombophilic risk factors, especially including dysfibrinogenemia, heparin cofactor II, thrombomodulin, lipoprotein(a), sticky platelet syndrome, plasminogen activator inhibitor-1 apolipoprotein E, tissue factor pathway inhibitor, paroxysmal nocturnal haemoglobinuria and heparin-induced thrombocytopenia.

Role of DNA copy number variation in dyslipidemias

PURPOSE OF REVIEW

DNA copy number variations (CNVs) are quantitative structural rearrangements that include deletions, duplications, and higher order amplifications. Because of technical limitations, the contribution of this common form of genetic variation to regulation of lipid metabolism and dyslipidemia has been underestimated.

RECENT FINDINGS

Recent literature involving CNVs and dyslipidemias has focused mainly on rare CNVs causing familial hypercholesterolemia, and a common CNV polymorphism as the major determinant of lipoprotein(a) plasma concentrations. Additionally, there is tantalizing evidence of largely uninvestigated but plausible presence of CNVs underlying other dyslipidemias. We also discuss the future role of improved technologies in facilitating more economic, routine CNV assessment in dyslipidemias.

SUMMARY

CNVs account for large proportion of human genetic variation and are already known to contribute to susceptibility of dyslipidemias, particularly in about 10% of familial hypercholesterolemia patients. Increasing availability of clinical next-generation sequencing and bioinformatics presents a cost-effective opportunity for novel CNV discoveries in dyslipidemias.

Lipoprotein(a): the revenant

In the mid-1990s, the days of lipoprotein(a) [Lp(a)] were numbered and many people would not have placed a bet on this lipid particle making it to the next century. However, genetic studies brought Lp(a) back to the front-stage after a Mendelian randomization approach used for the first time provided strong support for a causal role of high Lp(a) concentrations in cardiovascular disease and later also for aortic valve stenosis. This encouraged the use of therapeutic interventions to lower Lp(a) as well numerous drug developments, although these approaches mainly targeted LDL cholesterol, while the Lp(a)-lowering effect was only a 'side-effect'. Several drug developments did show a potent Lp(a)-lowering effect but did not make it to endpoint studies, mainly for safety reasons. Currently, three therapeutic approaches are either already in place or look highly promising: (i) lipid apheresis (specific or unspecific for Lp(a)) markedly decreases Lp(a) concentrations as well as cardiovascular endpoints; (ii) PCSK9 inhibitors which, besides lowering LDL cholesterol also decrease Lp(a) by roughly 30%; and (iii) antisense therapy targeting apolipoprotein(a) which has shown to specifically lower Lp(a) concentrations by up to 90% in phase 1 and 2 trials without influencing other lipids. Until the results of phase 3 outcome studies are available for antisense therapy, we will have to exercise patience, but with optimism since never before have we had the tools we have now to prove Koch's extrapolated postulate that lowering high Lp(a) concentrations might be protective against cardiovascular disease.

Genome-wide analysis yields new loci associating with aortic valve stenosis

Aortic valve stenosis (AS) is the most common valvular heart disease, and valve replacement is the only definitive treatment. Here we report a large genome-wide association (GWA) study of 2,457 Icelandic AS cases and 349,342 controls with a follow-up in up to 4,850 cases and 451,731 controls of European ancestry. We identify two new AS loci, on chromosome 1p21 near PALMD (rs7543130; odds ratio (OR) = 1.20, P = 1.2 × 10⁻²²) and on chromosome 2q22 in TEX41 (rs1830321; OR = 1.15, P = 1.8 × 10⁻¹³). Rs7543130 also associates with bicuspid aortic valve (BAV) (OR = 1.28, P = 6.6 × 10⁻¹⁰) and aortic root diameter (P = 1.30 × 10⁻⁸), and rs1830321 associates with BAV (OR = 1.12, P = 5.3 × 10⁻³) and coronary artery disease (OR = 1.05, P = 9.3 × 10⁻⁵). The results implicate both cardiac developmental abnormalities and atherosclerosis-like processes in the pathogenesis of AS. We show that several pathways are shared by CAD and AS. Causal analysis suggests that the shared risk factors of Lp(a) and non-high-density lipoprotein cholesterol contribute substantially to the frequent co-occurence of these diseases.

Aortic valve stenosis (AS) is the most common valvular heart disease. Here the authors identify two new AS loci that also associate with bicuspid aortic valve, aortic root diameter and/or coronary artery disease implicating both developmental abnormalities and atherosclerosis-like processes in AS.

Cohort profile: the Emory Cardiovascular Biobank (EmCAB)

PURPOSE

The Emory Cardiovascular Biobank (EmCAB) is an ongoing prospective registry of patients undergoing cardiac catheterisation, which was established to identify novel factors associated with the pathobiological process and treatment of cardiovascular disease.

PARTICIPANTS

Individuals aged 18 years and older undergoing cardiac catheterisation at three Emory Healthcare sites in Atlanta are asked to participate in this prospective registry. Around 95% agree to participate. Around 7000 unique patients have been enrolled. The current data set contains detailed phenotyping, patient outcomes, genomics, protein biomarkers, regenerative markers, transcriptomic analysis, metabolomics profiling and longitudinal follow-up for adverse cardiovascular outcomes.

FINDINGS TO DATE

Thus far, the EmCAB has approximately 3000 major cardiovascular events. About 48% of the EmCAB participants have more than 5 years of follow-up. It is a great resource for discovery of novel predictive factors for cardiovascular disease outcomes, including genomics, transcriptomics, protein biomarkers, oxidative stress markers and circulating progenitor cells. Several circulating inflammatory markers have shown to improve risk prediction metrics beyond standard risk factors.

FUTURE PLANS

Future integrative -omics analyses will provide the cardiovascular research community opportunities for subsequent mechanistic confirmation studies, which will promote the development of effective personalised therapy that leads to clinical care tailored to the individual patient.

Lipoprotein(a) in clinical practice: New perspectives from basic and translational science

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for coronary heart disease (CHD) and calcific aortic valve stenosis (CAVS). Genetic, epidemiological and in vitro data provide strong evidence for a pathogenic role for Lp(a) in the progression of atherothrombotic disease. Despite these advancements and a race to develop new Lp(a) lowering therapies, there are still many unanswered and emerging questions about the metabolism and pathophysiology of Lp(a). New studies have drawn attention to Lp(a) as a contributor to novel pathogenic processes, yet the mechanisms underlying the contribution of Lp(a) to CVD remain enigmatic. New therapeutics show promise in lowering plasma Lp(a) levels, although the complete mechanisms of Lp(a) lowering are not fully understood. Specific agents targeted to apolipoprotein(a) (apo(a)), namely antisense oligonucleotide therapy, demonstrate potential to decrease Lp(a) to levels below the 30-50 mg/dL (75-150 nmol/L) CVD risk threshold. This therapeutic approach should aid in assessing the benefit of lowering Lp(a) in a clinical setting.

Uncertain thrombophilia markers

The development of venous thromboembolism (VTE), which includes deep-vein thrombosis and pulmonary embolism, may be associated with inherited or acquired risk factors that can be measured in plasma or DNA testing. The main inherited thrombophilias include the plasma deficiencies of the natural anticoagulants antithrombin, protein C and S; the gain-of-function mutations factor V Leiden and prothrombin G20210A; some dysfibrinogenaemias and high plasma levels of coagulation factor VIII. Besides these established biomarkers, which usually represent the first-level laboratory tests for thrombophilia screening, a number of additional abnormalities have been less consistently associated with an increased VTE risk. These uncertain causes of thrombophilias will be discussed in this narrative review, focusing on their clinical impact and the underlying pathogenetic mechanisms. Currently, there is insufficient ground to recommend their inclusion within the framework of conventional thrombophilia testing.

Characterization of the I4399M variant of apolipoprotein(a): implications for altered prothrombotic properties of lipoprotein(a)

Essentials Elevated lipoproteinp(a) is an independent and causal risk factor for atherothrombotic diseases. rs3798220 (Ile/Met substitution in apo(a) protease-like domain) is associated with disease risk. Recombinant I4399M apo(a) altered clot structure to accelerate coagulation/delay fibrinolysis. Evidence was found for increased solvent exposure and oxidation of Met residue.

SUMMARY

Background Lipoprotein(a) (Lp[a]) is a causal risk factor for a variety of cardiovascular diseases. Apolipoprotein(a) (apo[a]), the distinguishing component of Lp(a), is homologous with plasminogen, suggesting that Lp(a) can interfere with the normal fibrinolytic functions of plasminogen. This has implications for the persistence of fibrin clots in the vasculature and hence for atherothrombotic diseases. A single-nucleotide polymorphism (SNP) (rs3798220) in the gene encoding apo(a) has been reported that results in an Ile→Met substitution in the protease-like domain (I4399M variant). In population studies, the I4399M variant has been correlated with elevated plasma Lp(a) levels and higher coronary heart disease risk, and carriers of the SNP had increased cardiovascular benefit from aspirin therapy. In vitro studies suggested an antifibrinolytic role for Lp(a) containing this variant. Objectives We performed a series of experiments to assess the effect of the Ile→Met substitution on fibrin clot formation and lysis, and on the architecture of the clots. Results We found that the Met variant decreased coagulation time and increased fibrin clot lysis time as compared with wild-type apo(a). Furthermore, we observed that the presence of the Met variant significantly increased fibrin fiber width in plasma clots formed ex vivo, while having no effect on fiber density. Mass spectrometry analysis of a recombinant apo(a) species containing the Met variant revealed sulfoxide modification of the Met residue. Conclusions Our data suggest that the I4399M variant differs structurally from wild-type apo(a), which may underlie key differences related to its effects on fibrin clot architecture and fibrinolysis.

Emerging Therapeutic Options for Lowering of Lipoprotein(a): Implications for Prevention of Cardiovascular Disease

PURPOSE OF REVIEW

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are an independent and causal risk factor for cardiovascular diseases including coronary artery disease, ischemic stroke, and calcific aortic valve stenosis. This review summarizes the rationale for Lp(a) lowering and surveys relevant clinical trial data using a variety of agents capable of lowering Lp(a).

RECENT FINDINGS

Contemporary guidelines and recommendations outline populations of patients who should be screened for elevated Lp(a) and who might benefit from Lp(a) lowering. Therapies including drugs and apheresis have been described that lower Lp(a) levels modestly (∼20 %) to dramatically (∼80 %). Existing therapies that lower Lp(a) also have beneficial effects on other aspects of the lipid profile, with the exception of Lp(a)-specific apheresis and an antisense oligonucleotide that targets the mRNA encoding apolipoprotein(a). No clinical trials conducted to date have managed to answer the key question of whether Lp(a) lowering confers a benefit in terms of ameliorating cardiovascular risk, although additional outcome trials of therapies that lower Lp(a) are ongoing. It is more likely, however, that Lp(a)-specific agents will provide the most appropriate approach for addressing this question.

A Test in Context: Lipoprotein(a): Diagnosis, Prognosis, Controversies, and Emerging Therapies

Evidence that elevated lipoprotein(a) (Lp[a]) levels contribute to cardiovascular disease (CVD) and calcific aortic valve stenosis (CAVS) is substantial. Development of isoform-independent assays, in concert with genetic, epidemiological, translational, and pathophysiological insights, have established Lp(a) as an independent, genetic, and likely causal risk factor for CVD and CAVS. These observations are consistent across a broad spectrum of patients, risk factors, and concomitant therapies, including patients with low-density lipoprotein cholesterol <70 mg/dl. Statins tend to increase Lp(a) levels, possibly contributing to the "residual risk" noted in outcomes trials and at the bedside. Recently approved proprotein convertase subtilisin/kexin-type 9 inhibitors and mipomersen lower Lp(a) 20% to 30%, and emerging RNA-targeted therapies lower Lp(a) >80%. These approaches will allow testing of the "Lp(a) hypothesis" in clinical trials. This review summarizes the current landscape of Lp(a), discusses controversies, and reviews emerging therapies to reduce plasma Lp(a) levels to decrease risk of CVD and CAVS.

Relations between lipoprotein(a) concentrations, LPA genetic variants, and the risk of mortality in patients with established coronary heart disease: a molecular and genetic association study

BACKGROUND

Lipoprotein(a) concentrations in plasma are associated with cardiovascular risk in the general population. Whether lipoprotein(a) concentrations or LPA genetic variants predict long-term mortality in patients with established coronary heart disease remains less clear.

METHODS

We obtained data from 3313 patients with established coronary heart disease in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study. We tested associations of tertiles of lipoprotein(a) concentration in plasma and two LPA single-nucleotide polymorphisms ([SNPs] rs10455872 and rs3798220) with all-cause mortality and cardiovascular mortality by Cox regression analysis and with severity of disease by generalised linear modelling, with and without adjustment for age, sex, diabetes diagnosis, systolic blood pressure, BMI, smoking status, estimated glomerular filtration rate, LDL-cholesterol concentration, and use of lipid-lowering therapy. Results for plasma lipoprotein(a) concentrations were validated in five independent studies involving 10 195 patients with established coronary heart disease. Results for genetic associations were replicated through large-scale collaborative analysis in the GENIUS-CHD consortium, comprising 106 353 patients with established coronary heart disease and 19 332 deaths in 22 studies or cohorts.

FINDINGS

The median follow-up was 9·9 years. Increased severity of coronary heart disease was associated with lipoprotein(a) concentrations in plasma in the highest tertile (adjusted hazard radio [HR] 1·44, 95% CI 1·14-1·83) and the presence of either LPA SNP (1·88, 1·40-2·53). No associations were found in LURIC with all-cause mortality (highest tertile of lipoprotein(a) concentration in plasma 0·95, 0·81-1·11 and either LPA SNP 1·10, 0·92-1·31) or cardiovascular mortality (0·99, 0·81-1·2 and 1·13, 0·90-1·40, respectively) or in the validation studies.

INTERPRETATION

In patients with prevalent coronary heart disease, lipoprotein(a) concentrations and genetic variants showed no associations with mortality. We conclude that these variables are not useful risk factors to measure to predict progression to death after coronary heart disease is established.

FUNDING

Seventh Framework Programme for Research and Technical Development (AtheroRemo and RiskyCAD), INTERREG IV Oberrhein Programme, Deutsche Nierenstiftung, Else-Kroener Fresenius Foundation, Deutsche Stiftung für Herzforschung, Deutsche Forschungsgemeinschaft, Saarland University, German Federal Ministry of Education and Research, Willy Robert Pitzer Foundation, and Waldburg-Zeil Clinics Isny.

Peripheral Atheromatous Arterial Disease in the Young: Risk Factors, Clinical Features, and Prognosis From the COPART Cohort

We describe the cardiovascular risk factors, clinical presentation, and prognosis in a comparative study of patients with peripheral artery disease (PAD) from the Cohorte des Patients ARTériopathes (COPART) cohort, which includes patients hospitalized for PAD in France. Among the 2514 patients included in the cohort, 189 had PAD before or at the age of 50 years and 2325 had it after. Young patients with PAD had diabetes less frequently (34% vs 46%, P < .001), were more frequent active smokers (58% vs 23%, P < 0.001), had lower high-density lipoprotein cholesterol (HDL-C; 41 ± 14 vs 44 ± 15 mg/dL, P = .026), and had a less frequent family and personal history of coronary heart disease. In a subset of 59 patients whose lipoprotein (a) (Lp(a)) was measured, the Lp(a) levels were higher in the young patients than in the older ones (89.7 mg/dL [9.7-151.3] vs 19.9 mg/dL [3.0-207.9], P = .004). Survival and amputation-free survival was 2.2 times higher (1.5-3.2, P < .001) in the young after 1 year. The onset of PAD before 50 years was associated with active smoking, low HDL-C, high Lp(a), and lower mortality.

Genetic risk models: Influence of model size on risk estimates and precision

Disease risk estimation plays an important role in disease prevention. Many studies have found that the ability to predict risk improves as the number of risk single-nucleotide polymorphisms (SNPs) in the risk model increases. However, the width of the confidence interval of the risk estimate is often not considered in the evaluation of the risk model. Here, we explore how the risk and the confidence interval width change as more SNPs are added to the model in the order of decreasing effect size, using both simulated data and real data from studies of abdominal aortic aneurysms and age-related macular degeneration. Our results show that confidence interval width is positively correlated with model size and the majority of the bigger models have wider confidence interval widths than smaller models. Once the model size is bigger than a certain level, the risk does not shift markedly, as 100% of the risk estimates of the one-SNP-bigger models lie inside the confidence interval of the one-SNP-smaller models. We also created a confidence interval-augmented reclassification table. It shows that both more effective SNPs with larger odds ratios and less effective SNPs with smaller odds ratios contribute to the correct decision of whom to screen. The best screening strategy is selected and evaluated by the net benefit quantity and the reclassification rate. We suggest that individuals whose upper bound of their risk confidence interval is above the screening threshold, which corresponds to the population prevalence of the disease, should be screened.

Phenotypic Characterization of Genetically Lowered Human Lipoprotein(a) Levels

BACKGROUND

Genomic analyses have suggested that the LPA gene and its associated plasma biomarker, lipoprotein(a) (Lp[a]), represent a causal risk factor for coronary heart disease (CHD). As such, lowering Lp(a) levels has emerged as a therapeutic strategy. Beyond target identification, human genetics may contribute to the development of new therapies by defining the full spectrum of beneficial and adverse consequences and by developing a dose-response curve of target perturbation.

OBJECTIVES

The goal of this study was to establish the full phenotypic impact of LPA gene variation and to estimate a dose-response curve between genetically altered plasma Lp(a) and risk for CHD.

METHODS

We leveraged genetic variants at the LPA gene from 3 data sources: individual-level data from 112,338 participants in the U.K. Biobank; summary association results from large-scale genome-wide association studies; and LPA gene sequencing results from case subjects with CHD and control subjects free of CHD.

RESULTS

One SD genetically lowered Lp(a) level was associated with a 29% lower risk of CHD (odds ratio [OR]: 0.71; 95% confidence interval [CI]: 0.69 to 0.73), a 31% lower risk of peripheral vascular disease (OR: 0.69; 95% CI: 0.59 to 0.80), a 13% lower risk of stroke (OR: 0.87; 95% CI: 0.79 to 0.96), a 17% lower risk of heart failure (OR: 0.83; 95% CI: 0.73 to 0.94), and a 37% lower risk of aortic stenosis (OR: 0.63; 95% CI: 0.47 to 0.83). We observed no association with 31 other disorders, including type 2 diabetes and cancer. Variants that led to gain of LPA gene function increased the risk for CHD, whereas those that led to loss of gene function reduced the CHD risk.

CONCLUSIONS

Beyond CHD, genetically lowered Lp(a) levels are associated with a lower risk of peripheral vascular disease, stroke, heart failure, and aortic stenosis. As such, pharmacological lowering of plasma Lp(a) may influence a range of atherosclerosis-related diseases.

Human Genetics and the Causal Role of Lipoprotein(a) for Various Diseases

Lipoprotein(a) [Lp(a)] is a highly atherogenic lipoprotein that is under strong genetic control by the LPA gene locus. Genetic variants including a highly polymorphic copy number variation of the so called kringle IV repeats at this locus have a pronounced influence on Lp(a) concentrations. High concentrations of Lp(a) as well as genetic variants which are associated with high Lp(a) concentrations are both associated with cardiovascular disease which very strongly supports causality between Lp(a) concetrations and cardiovascular disease. This method of using a genetic variant that has a pronounced influence on a biomarker to support causality with an outcome is called Mendelian randomization approach and was applied for the first time two decades ago with data from Lp(a) and cardiovascular disease. This approach was also used to demonstrate a causal association between high Lp(a) concentrations and aortic valve stenosis, between low concentrations and type-2 diabetes mellitus and to exclude a causal association between Lp(a) concentrations and venous thrombosis. Considering the high frequency of these genetic variants in the population makes Lp(a) the strongest genetic risk factor for cardiovascular disease identified so far. Promising drugs that lower Lp(a) are on the horizon but their efficacy in terms of reducing clinical outcomes still has to be shown.

Lipoprotein (a) level, apolipoprotein (a) size, and risk of unexplained ischemic stroke in young and middle-aged adults

BACKGROUND AND AIMS

Circulating lipoprotein (a) [Lp(a)] level relates inversely to apolipoprotein (a) [apo(a)] size. Both smaller apo(a) isoforms and higher Lp(a) levels have been linked to coronary heart disease and stroke, but their independent contributions are less well defined. We examined the role of Lp(a) in younger adults with cryptogenic stroke.

METHODS

Lp(a) and apo(a) isoforms were evaluated in a prospectively designed case-control study of patients with unexplained ischemic stroke and stroke-free controls, ages 18 to 64. Serum Lp(a) was measured among 255 cases and 390 controls with both apo(a)-size independent and dependent assays. Apo(a) size was determined by agarose gel electrophoresis.

RESULTS

Cases and controls were similar in socio-demographic characteristics, but cases had more hypertension, diabetes, smoking, and migraine with aura. In race-specific analyses, Lp(a) levels showed positive associations with cryptogenic stroke in whites, but not in the smaller subgroups of blacks and Hispanics. After full adjustment, comparison of the highest versus lowest quartile in whites was significant for apo(a)-size-independent (OR = 2.10 [95% CI = 1.04, 4.27], p = 0.040), and near-significant for apo(a)-size-dependent Lp(a) (OR = 1.81 [95% CI = 0.95, 3.47], p = 0.073). Apo(a) size was not associated with cryptogenic stroke in any race-ethnic subgroup.

CONCLUSIONS

This study underscores the importance of Lp(a) level, but not apo(a) size, as an independent risk factor for unexplained ischemic stroke in young and middle-aged white adults. Given the emergence of effective Lp(a)-lowering therapies, these findings support routine testing for Lp(a) in this setting, along with further research to assess the extent to which such therapies improve outcomes in this population.

Lipoprotein(a) Levels in Patients With Abdominal Aortic Aneurysm

Circulating markers relevant to the development of abdominal aortic aneurysm (AAA) are currently required. Lipoprotein(a), Lp(a), is considered a candidate marker associated with the presence of AAA. The present meta-analysis aimed to evaluate the association between circulating Lp(a) levels and the presence of AAA. The PubMed-based search was conducted up to April 30, 2015, to identify the studies focusing on Lp(a) levels in patients with AAA and controls. Quantitative data synthesis was performed using a random effects model, with standardized mean difference (SMD) and 95% confidence interval (CI) as summary statistics. Overall, 9 studies were identified. After a combined analysis, patients with AAA were found to have a significantly higher level of Lp(a) compared to the controls (SMD: 0.87, 95% CI: 0.41-1.33, P < .001). This result remained robust in the sensitivity analysis, and its significance was not influenced after omitting each of the included studies from the meta-analysis. The present meta-analysis confirmed a higher level of circulating Lp(a) in patients with AAA compared to controls. High Lp(a) levels can be associated with the presence of AAA, and Lp(a) may be a marker in screening for AAA. Further studies are needed to establish the clinical utility of measuring Lp(a) in the prevention and management of AAA.

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

Relation of Plasma Lipoprotein(a) to Subclinical Coronary Plaque Volumes, Three-Vessel and Left Main Coronary Disease, and Severe Coronary Stenoses in Apparently Healthy African-Americans With a Family History of Early-Onset Coronary Artery Disease

Serum lipoprotein(a) [Lp(a)] is a coronary artery disease (CAD) risk factor in persons of European ancestry. Levels are twofold to threefold higher in African-Americans (AAs), but reported associations with CAD have been inconsistent. The relation of Lp(a) with the extent and severity of subclinical coronary plaque has not been described in AAs. We screened 269 apparently healthy AAs for risk factors and coronary plaque using advanced coronary computed tomographic angiography. Total coronary plaque (TCP), noncalcified coronary plaque, and calcified coronary plaque volumes (mm(3)) were quantified using a validated automated method. Lp(a) was measured by ELISA. Multivariable modeling was performed with adjustment for traditional CAD risk factors and intrafamilial correlations. Mean age was 51 ± 11 years and 64% were female. Plaque was present in 41%. Lp(a) was independently associated with TCP volume [log(TCP + 1)] (p = 0.04), 3-vessel and/or left main involvement (p = 0.04), and at least 1 stenosis >50% (p = 0.006). Best-fit regression analyses showed that subjects with Lp(a) >40 mg/dl were threefold more likely to have 3-vessel and/or left main disease (95% confidence interval 1.4 to 6.8, p = 0.005) and fourfold more likely to have stenosis >50% (95% confidence interval 1.3 to 15.0, p = 0.02). In subjects with plaque (n = 110), multivariable models showed the Lp(a) level was significantly and independently associated with TCP (p = 0.009), noncalcified coronary plaque (p = 0.01), and calcified coronary plaque (p = 0.003) and affected vessel length (p = 0.01). In conclusion, high Lp(a) is strongly associated with coronary plaque volumes, extent, and severity in apparently healthy AAs. High levels of Lp(a) may be particularly important in the pathogenesis of CAD in AAs.

Lipoprotein apheresis for the treatment of elevated circulating levels of lipoprotein(a): a critical literature review

Lipoprotein(a), which consists of a low-density lipoprotein (LDL) particle linked to an apolipoprotein(a) moiety, is currently considered an independent risk factor for cardiovascular disease due to its atherogenic (LDL-like) and prothrombotic (plasminogen-like) properties. The aim of this review is to provide an overview of the current and newer therapies for lowering increased lipoprotein(a) levels, focusing on lipoprotein apheresis. After a systematic literature search, we identified ten studies which, overall, documented that lipoprotein apheresis is effective in reducing increased lipoprotein(a) levels and cardiovascular events.

Functional Variant in the SLC22A3-LPAL2-LPA Gene Cluster Contributes to the Severity of Coronary Artery Disease

OBJECTIVE

Recent genome-wide association studies have identified that genetic variants in the SLC22A3-LPAL2-LPA gene cluster influence plasma lipoprotein(a) [Lp(a)] concentration. However, the association between this gene cluster and the severity of coronary artery disease (CAD), especially the potential underlying mechanism, remains unclear. The purpose of this study was to investigate the association between variation in the SLC22A3-LPAL2-LPA gene cluster and CAD.

APPROACH AND RESULTS

We performed 2-stage case-control studies in a Chinese Han population. The variant genotypes were examined for their association with both Lp(a) level and severity of CAD. Putative mechanisms were also evaluated. One single nucleotide polymorphism, rs3088442, in the SLC22A3-LPAL2-LPA gene cluster was significantly associated with both plasma Lp(a) levels and CAD severity. The gene dosage of the risk allele at rs3088442 indicated a robust association with left main trunk disease (P=0.046), number of vascular lesions (P=4.5×10(-3)), and Gensini scores (P=0.012) in patients with CAD. Reporter gene analysis indicated that the rs3088442 G allele might suppress miR-147a binding to the 3' untranslated region of SLC22A3, resulting in altered SLC22A3 and LPA gene expression (P=0.015 and 9.2×10(-6), respectively), possibly explaining the increased plasma Lp(a) levels and risk of CAD.

CONCLUSIONS

The genotype of rs3088442 within the SLC22A3-LPAL2-LPA gene cluster may contribute to regulation of plasma Lp(a) levels and possibly to the severity of CAD in a Chinese Han population.

Evidence-based assessment of lipoprotein(a) as a risk biomarker for cardiovascular diseases - Some answers and still many questions

The present article is aimed at outlining the current state of knowledge regarding the clinical value of lipoprotein(a) (Lp(a)) as a marker of cardiovascular disease (CVD) risk by summarizing the results of recent clinical studies, meta-analyses and systematic reviews. The literature supports the predictive value of Lp(a) on CVD outcomes, although the effect size is modest. Lp(a) would also appear to have an effect on cerebrovascular outcomes, however the effect appears even smaller than that for CVD outcomes. Consideration of apolipoprotein(a) (apo(a)) isoforms and LPA genetics in relation to the simple assessment of Lp(a) concentration may enhance clinical practice in vascular medicine. We also describe recent advances in Lp(a) research (including therapies) and highlight areas where further research is needed such as the measurement of Lp(a) and its involvement in additional pathophysiological processes.

Differential burden of rare protein truncating variants in Alzheimer's disease patients compared to centenarians

We compared coding region variants of 53 cognitively healthy centenarians and 45 patients with Alzheimer's disease (AD), all of Ashkenazi Jewish (AJ) ancestry. Despite the small sample size, the known AD risk variant APOE4 reached genome-wide significance, indicating the advantage of utilizing 'super-controls'. We restricted our subsequent analysis to rare variants observed at most once in the 1000 Genomes database and having a minor allele frequency below 2% in our AJ sample. We compared the burden of predicted protein altering variants between cases and controls as normalized by the level of rare synonymous variants. We observed an increased burden among AD subjects for predicted loss-of-function (LoFs) variants defined as stop-gain, frame shift, initiation codon (INIT) and splice site mutations (n = 930, OR = 1.3, P = 1.5×E-5). There was no enrichment across all rare protein altering variants defined as missense plus LoFs, in frame indels and stop-loss variants (n = 13 014, OR = 0.97, P = 0.47). Among LoFs, the strongest burden was observed for INIT (OR = 2.16, P = 0.0097) and premature stop variants predicted to cause non-sense-mediated decay in the majority of transcripts (NMD) (OR = 1.98, P = 0.02). Notably, this increased burden of NMD, INIT and splice variants was more pronounced in a set of 1397 innate immune genes (OR = 4.55, P = 0.0043). Further comparison to additional exomes indicates that the difference in LoF burden originated both from the AD and centenarian sample. In summary, we observed an overall increased burden of rare LoFs in AD subjects as compared to centenarians, and this enrichment is more pronounced for innate immune genes.

Sex-Specific Genetic Variants are Associated With Coronary Endothelial Dysfunction

Background

Endothelial dysfunction is an early stage of atherosclerosis. Single‐nucleotide polymorphisms (SNPs) have been associated with vascular dysfunction, cardiac events, and coronary artery remodeling. We aimed to detect SNPs associated with endothelial dysfunction and determine whether these associations are sex specific.

Methods and Results

Six hundred forty‐three subjects without significant obstructive coronary artery disease underwent invasive coronary endothelial function assessment. We collected data from 1536 SNPs that had previously been associated with vasoreactivity, angiogenesis, inflammation, artery calcification, atherosclerotic risk factors, insulin resistance, hormone levels, blood coagulability, or with coronary heart disease. Coronary vascular reactivity was assessed by the percent change in coronary artery diameter ≤ −20% after an intracoronary bolus injection of acetylcholine on invasive coronary physiology study. SNPs significantly associated with coronary epicardial endothelial dysfunction were ADORA1,KCNQ1, and DNAJC4 in the whole cohort, LPA, MYBPH, ADORA3, and PON1 in women and KIF6 and NFKB1 in men (P<0.01).

Conclusions

We have identified several significant SNPs that are associated with an increased risk of coronary endothelial dysfunction. These associations appear to be sex specific and may explain gender‐related differences in development of atherosclerosis.

Structure, function, and genetics of lipoprotein (a)

Lipoprotein (a) [Lp(a)] has attracted the interest of researchers and physicians due to its intriguing properties, including an intragenic multiallelic copy number variation in the LPA gene and the strong association with coronary heart disease (CHD). This review summarizes present knowledge of the structure, function, and genetics of Lp(a) with emphasis on the molecular and population genetics of the Lp(a)/LPA trait, as well as aspects of genetic epidemiology. It highlights the role of genetics in establishing Lp(a) as a risk factor for CHD, but also discusses uncertainties, controversies, and lack of knowledge on several aspects of the genetic Lp(a) trait, not least its function.

Understanding the pathogenesis of abdominal aortic aneurysms

An aortic aneurysm is a dilatation in which the aortic diameter is ≥3.0 cm. If left untreated, the aortic wall continues to weaken and becomes unable to withstand the forces of the luminal blood pressure resulting in progressive dilatation and rupture, a catastrophic event associated with a mortality of 50-80%. Smoking and positive family history are important risk factors for the development of abdominal aortic aneurysms (AAA). Several genetic risk factors have also been identified. On the histological level, visible hallmarks of AAA pathogenesis include inflammation, smooth muscle cell apoptosis, extracellular matrix degradation and oxidative stress. We expect that large genetic, genomic, epigenetic, proteomic and metabolomic studies will be undertaken by international consortia to identify additional risk factors and biomarkers, and to enhance our understanding of the pathobiology of AAA. Collaboration between different research groups will be important in overcoming the challenges to develop pharmacological treatments for AAA.

Apolipoprotein(a) Kringle-IV Type 2 Copy Number Variation Is Associated with Venous Thromboembolism

In addition to the established association between high lipoprotein(a) [Lp(a)] concentrations and coronary artery disease, an association between Lp(a) and venous thromboembolism (VTE) has also been described. Lp(a) is controlled by genetic variants in LPA gene, coding for apolipoprotein(a), including the kringle-IV type 2 (KIV-2) size polymorphism. Aim of the study was to investigate the role of LPA gene KIV-2 size polymorphism and single nucleotide polymorphisms (SNPs) (rs1853021, rs1800769, rs3798220, rs10455872) in modulating VTE susceptibility. Five hundred and sixteen patients with VTE without hereditary and acquired thrombophilia and 1117 healthy control subjects, comparable for age and sex, were investigated. LPA KIV-2 polymorphism, rs3798220 and rs10455872 SNPs were genotyped by TaqMan technology. Concerning rs1853021 and rs1800769 SNPs, PCR-RFLP assay was used. LPA KIV-2 repeat number was significantly lower in patients than in controls [median (interquartile range) 11(6–17) vs 15(9–25), p<0.0001]. A significantly higher prevalence of KIV-2 repeat number ≤7 was observed in patients than in controls (33.5% vs 15.5%, p<0.0001). KIV-2 repeat number was independently associated with VTE (p = 4.36 x10^-9), as evidenced by the general linear model analysis adjusted for transient risk factors. No significant difference in allele frequency for all SNPs investigated was observed. Haplotype analysis showed that LPA haplotypes rather than individual SNPs influenced disease susceptibility. Receiver operating characteristic curves analysis showed that a combined risk prediction model, including KIV-2 size polymorphism and clinical variables, had a higher performance in identifying subjects at VTE risk than a clinical-only model, also separately in men and women.

Lipoprotein (a): truly a direct prothrombotic factor in cardiovascular disease?

Elevated plasma concentrations of lipoprotein (a) [Lp(a)] have been determined to be a causal risk factor for coronary heart disease, and may similarly play a role in other atherothrombotic disorders. Lp(a) consists of a lipoprotein moiety indistinguishable from LDL, as well as the plasminogen-related glycoprotein, apo(a). Therefore, the pathogenic role for Lp(a) has traditionally been considered to reflect a dual function of its similarity to LDL, causing atherosclerosis, and its similarity to plasminogen, causing thrombosis through inhibition of fibrinolysis. This postulate remains highly speculative, however, because it has been difficult to separate the prothrombotic/antifibrinolytic functions of Lp(a) from its proatherosclerotic functions. This review surveys the current landscape surrounding these issues: the biochemical basis for procoagulant and antifibrinolytic effects of Lp(a) is summarized and the evidence addressing the role of Lp(a) in both arterial and venous thrombosis is discussed. While elevated Lp(a) appears to be primarily predisposing to thrombotic events in the arterial tree, the fact that most of these are precipitated by underlying atherosclerosis continues to confound our understanding of the true pathogenic roles of Lp(a) and, therefore, the most appropriate therapeutic target through which to mitigate the harmful effects of this lipoprotein.

New and emerging biomarkers in cardiovascular disease

Cardiovascular disease (CVD) is the most common cause of death and disability worldwide. Therefore, great importance has been placed on the discovery of novel risk factors and metabolic pathways relevant in the prevention and management of CVD. Such research is ongoing and may continue to lead to better risk stratification of individuals and/or the development of new intervention targets and treatment options. This review highlights emerging biomarkers related to lipid metabolism, glycemia, inflammation, and cardiac damage, some of which show promising associations with CVD risk and provide further understanding of the underlying pathophysiology. However, their measurement methodology and assays will require validation and standardization, and it will take time to accumulate evidence of their role in CVD in various population settings in order to fully assess their clinical utility. Several of the novel biomarkers represent intriguing, potentially game-changing targets for therapy.

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS

Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS

Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION

Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

An update on the etiology of abdominal aortic aneurysms: implications for future diagnostic testing

Abdominal aortic aneurysm (AAA) disease is multifactorial with both environmental and genetic risk factors. The current research in AAA revolves around genetic profiles and expression studies in both human and animal models. Variants in genes involved in extracellular matrix degradation, inflammation, the renin-angiotensin system, cell growth and proliferation and lipid metabolism have been associated with AAA using a variety of study designs. However, the results have been inconsistent and without a standard animal model for validation. Thus, despite the growing body of knowledge, the specific variants responsible for AAA development, progression and rupture have yet to be determined. This review explores some of the more significant genetic studies to provide an overview of past studies that have influenced the current understanding of AAA etiology. Expanding our understanding of disease pathogenesis will inform research into novel diagnostics and therapeutics and ultimately to improve outcomes for patients with AAA.