Analysis of the apo(a) size polymorphism in Asian Indian populations: association with Lp(a) concentration and coronary heart disease

Assessing causal associations of blood counts and biochemical indicators with pulmonary arterial hypertension: a Mendelian randomization study and results from national health and nutrition examination survey 2003-2018

Background

Blood counts and biochemical markers are among the most common tests performed in hospitals and most readily accepted by patients, and are widely regarded as reliable biomarkers in the literature. The aim of this study was to assess the causal relationship between blood counts, biochemical indicators and pulmonary arterial hypertension (PAH).

Methods

A two-sample Mendelian randomization (MR) analysis was performed to assess the causal relationship between blood counts and biochemical indicators with PAH. The genome-wide association study (GWAS) for blood counts and biochemical indicators were obtained from the UK Biobank (UKBB), while the GWAS for PAH were sourced from the FinnGen Biobank. Inverse variance weighting (IVW) was used as the primary analysis method, supplemented by three sensitivity analyses to assess the robustness of the results. And we conducted an observational study using data from National Health and Nutrition Examination Survey (NHANES) 2003-2018 to verify the relationship.

Results

The MR analysis primarily using the IVW method revealed genetic variants of platelet count (OR=2.51, 95% CI 1.56-4.22, P<0.001), platelet crit(OR=1.87, 95% CI1.17-7.65, P=0.022), direct bilirubin (DBIL)(OR=1.71, 95%CI 1.18-2.47,P=0.004), insulin-like growth factor (IGF-1)(OR=0.51, 95% CI 0.27-0.96, P=0.038), Lipoprotein A (Lp(a))(OR=0.66, 95% CI 0.45-0.98, P=0.037) and total bilirubin (TBIL)(OR=0.51, 95% CI 0.27-0.96, P=0.038) were significantly associated with PAH. In NHANES, multivariate logistic regression analyses revealed a significant positive correlation between platelet count and volume and the risk of PAH, and a significant negative correlation between total bilirubin and PAH.

Conclusion

Our study reveals a causal relationship between blood counts, biochemical indicators and pulmonary arterial hypertension. These findings offer novel insights into the etiology and pathological mechanisms of PAH, and emphasizes the important value of these markers as potential targets for the prevention and treatment of PAH.

Lipoprotein(a): a genetically determined risk factor for Cardiovascular disease

Lipoprotein(a) is a complex lipoprotein with unique characteristics distinguishing it from all the other apolipoprotein B-containing lipoprotein particles. Its lipid composition and the presence of a single molecule of apolipoprotein B per particle, render lipoprotein(a) similar to low-density lipoproteins. However, the presence of a unique, carbohydrate-rich protein termed apolipoprotein(a), linked by a covalent bond to apolipoprotein B imparts unique characteristics to lipoprotein(a) distinguishing it from all the other lipoproteins. Apolipoprotein(a) is highly polymorphic in size ranging in molecular weight from <300 KDa to >800 kDa. Both the size polymorphism and the concentration of lipoprotein(a) in plasma are genetically determined and unlike other lipoproteins, plasma concentration is minimally impacted by lifestyle modifications or lipid-lowering drugs. Many studies involving hundreds of thousands of individuals have provided strong evidence that elevated lipoprotein(a) is genetically determined and a causal risk factor for atherosclerotic cardiovascular disease. The concentration attained in adulthood is already present in children at around 5 years of age and therefore, those with elevated lipoprotein(a) are prematurely exposed to a high risk of cardiovascular disease. Despite the large number of guidelines and consensus statements on the management of lipoprotein(a) in atherosclerotic cardiovascular disease published in the last decade, lipoprotein(a) is still seldom measured in clinical settings. In this review, we provide an overview of the most important features that characterize lipoprotein(a), its role in cardiovascular disease, and the importance of adding the measurement of lipoprotein(a) for screening adults and youths to identify those at increased risk of atherosclerotic cardiovascular disease due to their elevated plasma concentration of lipoprotein(a).

Ancestry, Lipoprotein(a), and Cardiovascular Risk Thresholds: JACC Review Topic of the Week

This study reviews ancestral differences in the genetics of the LPA gene, risk categories of elevated lipoprotein(a) [Lp(a)] as defined by guidelines, ancestry-specific Lp(a) risk, absolute and proportional risk, predictive value of risk thresholds among different ancestries, and differences between laboratory vs clinical accuracy in Lp(a) assays. For clinical decision-making, the preponderance of evidence suggests that the predictive value of Lp(a) does not vary sufficiently to mandate the use of ancestry-specific risk thresholds. This paper interprets the literature on Lp(a) and ancestral risk to support: 1) clinicians on understanding cardiovascular disease risk in different ancestral groups; 2) trialists for the design of clinical trials to ensure adequate ancestral diversity to support broad conclusions of drug effects; 3) regulators in the evaluation of the design and interpretation of results of Lp(a)-lowering trials with different Lp(a) inclusion thresholds; and 4) clinical laboratories to measure Lp(a) by assays that discriminate risk thresholds appropriately.

Lipoprotein(a): A Genetically Determined, Causal, and Prevalent Risk Factor for Atherosclerotic Cardiovascular Disease: A Scientific Statement From the American Heart Association

High levels of lipoprotein(a) [Lp(a)], an apoB100-containing lipoprotein, are an independent and causal risk factor for atherosclerotic cardiovascular diseases through mechanisms associated with increased atherogenesis, inflammation, and thrombosis. Lp(a) is predominantly a monogenic cardiovascular risk determinant, with ≈70% to ≥90% of interindividual heterogeneity in levels being genetically determined. The 2 major protein components of Lp(a) particles are apoB100 and apolipoprotein(a). Lp(a) remains a risk factor for cardiovascular disease development even in the setting of effective reduction of plasma low-density lipoprotein cholesterol and apoB100. Despite its demonstrated contribution to atherosclerotic cardiovascular disease burden, we presently lack standardization and harmonization of assays, universal guidelines for diagnosing and providing risk assessment, and targeted treatments to lower Lp(a). There is a clinical need to understand the genetic and biological basis for variation in Lp(a) levels and its relationship to disease in different ancestry groups. This scientific statement capitalizes on the expertise of a diverse basic science and clinical workgroup to highlight the history, biology, pathophysiology, and emerging clinical evidence in the Lp(a) field. Herein, we address key knowledge gaps and future directions required to mitigate the atherosclerotic cardiovascular disease risk attributable to elevated Lp(a) levels.

Associations of serum apolipoprotein A1, B levels and their ratio with blood pressure in Chinese adults with coronary artery disease

OBJECTIVE

We examined the relationships of apolipoprotein A1 (ApoA1), ApoB levels and ApoB/A1 ratio with blood pressure (BP) in Chinese adults with coronary artery disease (CAD).

METHODS

This cross-sectional study included 4921 adults with CAD. SBP, DBP, serum ApoA1 and ApoB levels were measured. The associations between Apo and BP were assessed by analyses of covariance.

RESULTS

Serum ApoA1 was inversely associated with BP, whereas ApoB and the ApoB/A1 ratio exhibited positive associations with BP. For all subjects, a higher ApoA1 level was associated with lower SBP. Subjects in the fourth quartile for ApoA1 exhibited - 2.85 and - 2.63% lower DBP and mean arterial pressure (MAP), respectively than those in the third quartile. In contrast, higher ApoB and ApoB/A1 ratios were associated with higher SBP, DBP and MAP. The mean differences between ApoB quartiles 4 and 1 were 1.54% for SBP, 2.92% for DBP and 2.29% for MAP. The mean differences between the ApoB/A1 ratio quartiles 4 and 1 were 1.94% for SBP, 3.53% for DBP and 2.80% for MAP. In analyses stratified by gender, graded and inverse associations of ApoA1 with SBP, DBP and MAP were observed in both men and women, but positive associations were observed for ApoB and the ApoB/A1 ratio. Path analysis showed that BMI mediated the associations between ApoB and the ApoB/A1 ratio and SBP.

CONCLUSIONS

In general, serum ApoA1 was inversely associated with BP in persons with CAD. In contrast, serum ApoB and the ApoB/A1 ratio were positively associated with BP, and these associations were mediated by BMI.

Nonsynonymous SNPs in LPA homologous to plasminogen deficiency mutants represent novel null apo(a) alleles

Plasma lipoprotein (a) [Lp(a)] levels are largely determined by variation in the LPA gene, which codes for apo(a). Genome-wide association studies (GWASs) have identified nonsynonymous variants in LPA that associate with low Lp(a) levels, although their effect on apo(a) function is unknown. We investigated two such variants, R990Q and R1771C, which were present in four null Lp(a) individuals, for structural and functional effects. Sequence alignments showed the R990 and R1771 residues to be highly conserved and homologous to each other and to residues associated with plasminogen deficiency. Structural modeling showed both residues to make several polar contacts with neighboring residues that would be ablated on substitution. Recombinant expression of the WT and R1771C apo(a) in liver and kidney cells showed an abundance of an immature form for both apo(a) proteins. A mature form of apo(a) was only seen with the WT protein. Imaging of the recombinant apo(a) proteins in conjunction with markers of the secretory pathway indicated a poor transit of R1771C into the Golgi. Furthermore, the R1771C mutant displayed a glycosylation pattern consistent with ER, but not Golgi, glycosylation. We conclude that R1771 and the equivalent R990 residue facilitate correct folding of the apo(a) kringle structure and mutations at these positions prevent the proper folding required for full maturation and secretion. To our knowledge, this is the first example of nonsynonymous variants in LPA being causative of a null Lp(a) phenotype.

Looking at Lp(a) and Related Cardiovascular Risk: from Scientific Evidence and Clinical Practice

PURPOSE OF REVIEW

A considerable body of data from genetic and epidemiological studies strongly support a causal relationship between high lipoprotein(a) [Lp(a)] levels, and the development of atherosclerosis and cardiovascular disease. This relationship is continuous, unrelated to Lp(a) threshold, and independent of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol levels. Unfortunately, the mechanism(s) through which Lp(a) promotes atherosclerosis are not clarified yet. Suggested hypotheses include: an increased Lp(a)-associated cholesterol entrapment in the arterial intima followed by inflammatory cell recruitment, abnormal upload of proinflammatory oxidized phospholipids, impaired fibrinolysis by inhibition of plasminogen activation, and enhanced coagulation, through inhibition of the tissue factor pathway inhibitor. This review is aimed at summarizing the available evidence on the topic.

RECENT FINDINGS

There are two clinical forms, isolated hyperlipidemia(a) [HyperLp(a)] with acceptable LDL-C levels (< 70 mg/dL), and combined elevation of Lp(a) and LDL-C in plasma. To date, no drugs that selectively decrease Lp(a) are available. Some novel lipid-lowering drugs can lower Lp(a) levels, but to a limited extent, as their main effect is aimed at decreasing LDL-C levels. Significant Lp(a) lowering effects were obtained with nicotinic acid at high doses. However, adverse effects apart, nicotinic acid is no longer prescribed and available in Europe for clinical use, after European Agency of Medicines (EMA) ban. The only effective therapeutic option for now is Lipoprotein Apheresis (LA), albeit with some limitations. Lastly, it is to be acknowledged that the body of evidence confirming that reducing plasma isolated elevation of Lp(a) brings cardiovascular benefit is still insufficient. However, the growing bulk of clinical, genetic, mechanistic, and epidemiological available evidence strongly suggests that Lp(a) is likely to be the smoking gun.

Lipoprotein(a): An underrecognized genetic risk factor for malignant coronary artery disease in young Indians

Malignant coronary artery disease (CAD) refers to a severe and extensive atherosclerotic process involving multiple coronary arteries in young individuals (aged <45 years in men and <50 years in women) with a low or no burden of established risk factors. Indians, in general, develop acute myocardial infarction (AMI) about 10 years earlier; AMI rates are threefold to fivefold higher in young Indians than in other populations. Although established CAD risk factors have a predictive value, they do not fully account for the excessive burden of CAD in young Indians. Lipoprotein(a) (Lp(a)) is increasingly recognized as the strongest known genetic risk factor for premature CAD, with high levels observed in Indians with malignant CAD. High Lp(a) levels confer a twofold to threefold risk of CAD-a risk similar to that of established risk factors, including diabetes. South Asians have the second highest Lp(a) levels and the highest risk of AMI from the elevated levels, more than double the risk observed in people of European descent. Approximately 25% of Indians and other South Asians have elevated Lp(a) levels (≥50 mg/dl), rendering Lp(a) a risk factor of great importance, similar to or surpassing diabetes. Lp(a) measurement is ready for clinical use and should be an essential part of all CAD research in Indians.

South Asian Cardiovascular Disease & Cancer Risk: Genetics & Pathophysiology

South Asians (SAs) are at heightened risk for cardiovascular disease as compared to other ethnic groups, facing premature and more severe coronary artery disease, and decreased insulin sensitivity. This disease burden can only be partially explained by conventional risk factors, suggesting the need for a specific cardiovascular risk profile for SAs. Current research, as explored through a comprehensive literature review, suggests the existence of population specific genetic risk factors such as lipoprotein(a), as well as population specific gene modulating factors. This review catalogues the available research on cardiovascular disease and genetics, anthropometry, and pathophysiology, and cancer genetics among SAs, with a geographical focus on the U.S. A tailored risk profile will hinge upon population customized classification and treatment guidelines, informed by continued research.

Lipoprotein(a) and lipid profiles of patients awaiting coronary artery bypass graft; a cross sectional study

Background

Lipoprotein(a) (Lp(a)) excess is an independent risk factor of coronary artery disease (CAD) and have shown wide ethnic variations. Further, lipid parameters used in the assessment and management of risk factors for CAD may not reflect accurately the disease or severity if the patients are on pharmacological interventions when compared to Lp(a). Lp(a) levels of Sri Lankan CAD patients awaiting coronary artery bypass graft are not documented.

Methods

A cross sectional study was carried out with patients (n = 102) awaiting coronary artery bypass graft at a tertiary healthcare institution in Sri Lanka. Lp(a) was determined by immunoturbidimetric method (Konelab 20XT) and information on risk factors collected using a standardized questionnaire. The severity of CAD was determined by Gensini score. Lipid parameters and pharmacological treatment data were obtained from the Medical Records. Data were analysed using independent sample t-test, Pearson and Spearman tests respectively.

Results

Total cholesterol (TC), LDL cholesterol (LDLc) and HDL cholesterol (HDLc) of the total study sample (average ± SD) were, 150 ± 36 mg/dL, 92 ± 36 mg/dL and 34 ± 9 mg/dL respectively with no significant difference irrespective of being on pharmacological treatment or not. All lipid parameters were significantly high (p < 0.05) in females. The average Lp(a) was 50 ± 38 (SD) mg/dL with no significant difference in males or females independent of being on treatment (50 ± 39 mg/dL) or not (49 ± 39 mg/dL) and above the cut off value (30 mg/dL).

Conclusions

Despite pharmacological interventions 27 % of the study population had high LDLc and majority low HDLc. Mean Lp(a) was in excess irrespective of risk factors or being on treatment or not and is confirmed as an independent, potential marker for assessing the susceptibility for CAD especially in those with other intermediate risk factors but considered non-hyperlipidemic by conventional methods.

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.

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.

Lack of association of rs3798220 with small apolipoprotein(a) isoforms and high lipoprotein(a) levels in East and Southeast Asians

OBJECTIVE

The variant allele of rs3798220 in the apolipoprotein(a) gene (LPA) is used to assess the risk for coronary artery disease (CAD) in Europeans, where it is associated with short alleles of the Kringle IV-2 (KIV-2) copy number variation (CNV) and high lipoprotein(a) (Lp(a)) concentrations. No association of rs3798220 with CAD was detected in a GWAS of East Asians. Our study investigated the association of rs3798220 with Lp(a) concentrations and KIV-2 CNV size in non-European populations to explain the missing association of the variant with CAD in Asians.

METHODS

We screened three populations from Africa and seven from Asia by TaqMan Assay for rs3798220 and determined KIV-2 CNV sizes of LPA alleles by pulsed-field gel electrophoresis (PFGE). Additionally, CAD cases from India were analysed. To investigate the phylogenetic origin of rs3798220, 40 LPA alleles from Chinese individuals were separated by PFGE and haplotyped for further SNPs.

RESULTS

The variant was not found in Africans. Allele frequencies in East and Southeast Asians ranged from 2.9% to 11.6%, and were very low (0.15%) in CAD cases and controls from India. The variant was neither associated with short KIV-2 CNV alleles nor elevated Lp(a) concentrations in Asians.

CONCLUSION

Our study shows that rs3798220 is no marker for short KIV-2 CNV alleles and high Lp(a) in East and Southeast Asians, although the haplotype background is shared with Europeans. It appears unlikely that this SNP confers atherogenic potential on its own. Furthermore, this SNP does not explain Lp(a) attributed risk for CAD in Asian Indians.

Lipoprotein (a): a Unique Independent Risk Factor for Coronary Artery Disease

The current epidemic affecting Indians is coronary artery disease (CAD), and is currently one of the most common causes of mortality and morbidity in developed and developing countries. The higher rate of CAD in Indians, as compared to people of other ethnic origin, may indicate a possible genetic susceptibility. Hence, Lp(a), an independent genetic risk marker for atherosclerosis and cardiovascular disease assumes great importance. Lp(a), an atherogenic lipoprotein, contains a cholesterol rich LDL particle, one molecule of apolipoprotein B-100 and a unique protein, apolipoprotein (a) which distinguishes it from LDL. Apo(a) is highly polymorphic and an inverse relationship between Lp(a) concentration and apo(a) isoform size has been observed. This is genetically controlled suggesting a functional diversity among the apo(a) isoforms. The LPA gene codes for apo(a) whose genetic heterogeneity is due to variations in its number of kringles. The exact pathogenic mechanism of Lp(a) is still not completely elucidated, but the structural homology of Lp(a) with LDL and plasmin is possibly responsible for its acting as a link between atherosclerosis and thrombosis. Upper limits of normal Lp(a) levels have not been defined for the Indian population. A cut off limit of 20 mg/dL has been suggested while for the Caucasian population it is 30 mg/dL. Though a variety of assays are available for its measurement, standardization of the analytical method is highly complicated as a majority of the methods are affected by the heterogeneity in apo(a) size. No therapeutic drug selectively targets Lp(a) but recently, new modifiers of apo(a) synthesis are being considered.

Lipoprotein ratios as surrogate markers for insulin resistance in South indians with normoglycemic nondiabetic acute coronary syndrome

Background. Insulin resistance has been associated with dyslipidemia and cardiovascular disease. Even though homeostasis model assessment of insulin resistance (HOMA-IR) is a well-known insulin resistance predictor, estimation of serum lipoprotein ratios has been recently suggested as a surrogate marker for insulin resistance. Here, we evaluated the relationship between lipoprotein ratios and insulin resistance in normoglycemic nondiabetic south Indians with acute coronary syndrome. Methods. 100 normoglycemic nondiabetic ACS patients and 140 controls were enrolled in the study. Levels of fasting glucose, fasting insulin, and lipid profile [total cholesterol (TC), triglycerides (TG), and high density lipoprotein cholesterol (HDL-C)], lipoprotein(a) [Lp(a)] levels were measured and lipoprotein ratios were computed. HOMA-IR was used to calculate the insulin resistance. Receiver operating characteristic curves (ROC) analysis was used to compare the power of these lipoprotein ratios to predict insulin resistance. Results. Lipoprotein ratios were significantly higher in normoglycemic nondiabetic ACS patients, as compared to healthy controls, and were significantly correlated with HOMA-IR by Spearman's rank correlation analysis. ROC curve showed that Lp(a)/HDL-C and TG/HDL-C ratios were the best surrogate predictors of insulin resistance in normoglycemic nondiabetic ACS. Conclusion. This study demonstrates that serum lipoprotein ratios significantly correlate with insulin resistance in normoglycemic nondiabetic ACS. Lp(a)/HDL-C and TG/HDL-C ratios could be used as surrogate markers of insulin resistance in atherosclerosis-prone south Indians with normoglycemic nondiabetic ACS.

Relook at lipoprotein (A): independent risk factor of coronary artery disease in north Indian population

AIMS

Lipoprotein (a) [Lp(a)] levels have shown wide ethnic variations. Sparse data on mean Lp(a) levels, its link with clinical variables and severity of coronary artery disease (CAD) in North Indian population needed further studies.

METHODS

150 patients, each of single vessel disease (SVD), double vessel disease (DVD) and triple vessel disease (TVD) with 150 healthy controls were drawn for the study. Serum Lp(a) estimation was performed by immunoturbidimetric method.

RESULTS

Lp(a) had a skewed distribution. Median Lp(a) level was significantly raised in cases as compared to controls (median 30.30 vs. 20 mg/dl, p < 0.001). Cases with acute coronary syndrome (ACS, 55.8%) had significantly higher median Lp(a) levels as compared to those with chronic stable angina (35.4 mg/dl vs. 23 mg/dl, p < 0.001). Significant difference in median Lp(a) levels were observed in patients with DVD or TVD versus control (30, 39.05 vs 20 mg/dl, p < 0.008). Lp(a) level was found to be an independent risk factor for CAD (AOR{adjusted odds ratio} 1.018, 95% CI 1.010-1.027; p < 0.001). Analysis using Lp(a) as categorical variable showed that progressive increase in Lp(a) concentration was associated with increased risk of CAD [AOR from lowest to highest quartile (1, 1.04, 1.43 and 2.65, p value for trend = 0.00026)]. Multivariably AOR of CAD for subjects with Lp(a) in the highest quartile (above 40 mg/dl) compared to those with Lp(a) ≤40 mg/dl was 2.308 (95% CI 1.465-3.636, p < 0.001).

CONCLUSION

Lp(a) above 40 mg/dl (corresponding to 75th percentile)assessed by an isoform insensitive assay is an independent risk factor for CAD. Raised Lp(a) level is also associated with increased risk of ACS and multivessel CAD.

When should we measure lipoprotein (a)?

Recently published epidemiological and genetic studies strongly suggest a causal relationship of elevated concentrations of lipoprotein (a) [Lp(a)] with cardiovascular disease (CVD), independent of low-density lipoproteins (LDLs), reduced high density lipoproteins (HDL), and other traditional CVD risk factors. The atherogenicity of Lp(a) at a molecular and cellular level is caused by interference with the fibrinolytic system, the affinity to secretory phospholipase A2, the interaction with extracellular matrix glycoproteins, and the binding to scavenger receptors on macrophages. Lipoprotein (a) plasma concentrations correlate significantly with the synthetic rate of apo(a) and recent studies demonstrate that apo(a) expression is inhibited by ligands for farnesoid X receptor. Numerous gaps in our knowledge on Lp(a) function, biosynthesis, and the site of catabolism still exist. Nevertheless, new classes of therapeutic agents that have a significant Lp(a)-lowering effect such as apoB antisense oligonucleotides, microsomal triglyceride transfer protein inhibitors, cholesterol ester transfer protein inhibitors, and PCSK-9 inhibitors are currently in trials. Consensus reports of scientific societies are still prudent in recommending the measurement of Lp(a) routinely for assessing CVD risk. This is mainly caused by the lack of definite intervention studies demonstrating that lowering Lp(a) reduces hard CVD endpoints, a lack of effective medications for lowering Lp(a), the highly variable Lp(a) concentrations among different ethnic groups and the challenges associated with Lp(a) measurement. Here, we present our view on when to measure Lp(a) and how to deal with elevated Lp(a) levels in moderate and high-risk individuals.

Lipoprotein(a): resurrected by genetics

Plasma lipoprotein(a) [Lp(a)] is a quantitative genetic trait with a very broad and skewed distribution, which is largely controlled by genetic variants at the LPA locus on chromosome 6q27. Based on genetic evidence provided by studies conducted over the last two decades, Lp(a) is currently considered to be the strongest genetic risk factor for coronary heart disease (CHD). The copy number variation of kringle IV in the LPA gene has been strongly associated with both Lp(a) levels in plasma and risk of CHD, thereby fulfilling the main criterion for causality in a Mendelian randomization approach. Alleles with a low kringle IV copy number that together have a population frequency of 25-35% are associated with a doubling of the relative risk for outcomes, which is exceptional in the field of complex genetic phenotypes. The recently identified binding of oxidized phospholipids to Lp(a) is considered as one of the possible mechanisms that may explain the pathogenicity of Lp(a). Drugs that have been shown to lower Lp(a) have pleiotropic effects on other CHD risk factors, and an improvement of cardiovascular endpoints is up to now lacking. However, it has been established in a proof of principle study that lowering of very high Lp(a) by apheresis in high-risk patients with already maximally reduced low-density lipoprotein cholesterol levels can dramatically reduce major coronary events.

Lipoprotein(a): more interesting than ever after 50 years

PURPOSE OF REVIEW

Lipoprotein(a) [Lp(a)] is a risk factor for cardiovascular disease; we highlight the most recent research initiatives that have sought to define Lp(a)-dependent pathogenicity as well as pharmacologic approaches to lowering Lp(a).

RECENT FINDINGS

Recent large-scale meta-analyses have confirmed elevated Lp(a) concentrations to be a moderate but consistent prospective coronary heart disease (CHD) risk factor. The Mendelian randomization approach has also associated LPA variants with Lp(a) concentration and CHD risk. Discoveries linking Lp(a) to oxidized phospholipid burden have implicated a proinflammatory role for Lp(a) hinting at a new mechanism underlying the association with CHD risk, which adds to previous atherogenic and thrombogenic mechanisms. Most existing Lp(a)-lowering drug treatments almost always show simultaneous effects on other lipoproteins, making it difficult to assign any clinical outcome specifically to the effects of Lp(a) lowering. Early experiments with antisense oligonucleotides targeting apolipoprotein(a) mRNA seem to indicate the pleiotropic effects of Lp(a) reduction on LDL and HDL in mice. The mechanism linking Lp(a) concentration with concentrations of other blood lipids remains unknown but may provide an insight into Lp(a) metabolism.

SUMMARY

Despite the wealth of epidemiologic evidence supporting Lp(a) concentration as a CHD risk factor, the lack of a definitive functional mechanism involving an Lp(a)-dependent pathway in CHD pathogenesis has limited the potential clinical connotation of Lp(a). However, the application of novel technologies to the long-standing mysteries of Lp(a) biology seems to provide the opportunity for expanding our understanding of Lp(a) and its complex role in cardiovascular health.

Do We Know When and How to Lower Lipoprotein(a)?

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OPINION STATEMENT

Currently, there are significant data to support a link between lipoprotein(a) [Lp(a)] levels and cardiovascular risk. However, there has not been a clinical trial examining the effects of Lp(a) reduction on cardiovascular risk in a primary prevention population. Until such a trial is conducted, current consensus supports using an Lp(a) percentile greater than 75% for race and gender as a risk stratification tool to target more aggressive low-density lipoprotein cholesterol (LDL-C) or apolipoprotein B (apoB) goals. Therefore, Lp(a) measurements should be considered in the following patients: individuals with early-onset vascular disease determined by clinical presentation or subclinical imaging, intermediate and high Framingham risk patients with a family history of premature coronary disease, and low Framingham risk patients with a family history and low high-density lipoprotein cholesterol (HDL-C) levels. Once LDL-C goals are met, Lp(a) levels may be taken into account in selecting secondary agents to reach more aggressive secondary goals, including non-HDL-C and apoB. To achieve Lp(a) reduction, one evidence-based approach is to initiate therapy with low-dose aspirin and extended-release niacin, titrated from 0.5 g up to 2 g over several weeks. If higher doses of niacin are desired, crystalline niacin allows for titration to a dosage as high as 2 g three times a day; however, the flushing side effect usually is quite prominent. Although hormone replacement therapy (HRT) has been shown to lower Lp(a), there are no indications for using HRT for primary or secondary prevention; therefore, we do not advocate initiating it solely for Lp(a) reduction. LDL apheresis is an option to lower LDL-C levels in patients with homozygous familial hypercholesterolemia who are not responsive to medical therapy. Although it does lower Lp(a), there is no treatment indication for this. A recent study supports the cholesterol absorption inhibitor ezetimibe's ability to lower Lp(a), a finding that deserves further investigation as it has not been previously reported in multiple ezetimibe trials. Additionally, the apoB messenger RNA antisense therapy mipomersen currently is in phase 3 trials and may serve as a potential inhibitor of Lp(a) production. Ultimately, more trial evidence is needed to determine whether lowering Lp(a) actually reduces cardiovascular risk, although this may be difficult to isolate without a specific Lp(a)-lowering therapy.

Lipoprotein(a): genotype-phenotype relationship and impact on atherogenic risk

In 2010, more than 45 years after the initial discovery of lipoprotein(a) [Lp(a)] by Kare Berg, an European Atherosclerosis Society Consensus Panel recommended screening for elevated Lp(a) in people at moderate to high risk of atherosclerotic cardiovascular disease (CVD). This recommendation was based on extensive epidemiological findings demonstrating a significant association between elevated plasma Lp(a) levels and coronary heart disease, myocardial infarction, and stroke. In addition to those patients considered to be at moderate to high risk of heart disease, statin-treated patients with recurrent heart disease were also identified as targeted for screening of elevated Lp(a) levels. Taken together, recent findings have significantly strengthened the notion of Lp(a) as a causal risk factor for CVD. It is well established that Lp(a) levels are largely determined by the size of the apolipoprotein a [apo(a)] gene; however, recent studies have identified several other LPA gene polymorphisms that have significant associations with an elevated Lp(a) level and a reduced copy number of K4 repeats. In addition, the contribution of other genes in regulating Lp(a) levels has been described. Besides the strong genetic regulation, new evidence has emerged regarding the impact of inflammation as a modulator of Lp(a) risk factor properties. Thus, oxidized phospholipids that possess a strong proinflammatory potential are preferentially carried on Lp(a) particles. Collectively, these findings point to the importance of both phenotypic and genotypic factors in influencing apo(a) proatherogenic properties. Therefore, studies taking both of these factors into account determining the amount of Lp(a) associated with each individual apo(a) size allele are valuable tools when assessing a risk factor role of Lp(a).

Lipoprotein(a) levels, apo(a) isoform size, and coronary heart disease risk in the Framingham Offspring Study

The aim of this study was to assess the independent contributions of plasma levels of lipoprotein(a) (Lp(a)), Lp(a) cholesterol, and of apo(a) isoform size to prospective coronary heart disease (CHD) risk. Plasma Lp(a) and Lp(a) cholesterol levels, and apo(a) isoform size were measured at examination cycle 5 in subjects participating in the Framingham Offspring Study who were free of CHD. After a mean follow-up of 12.3 years, 98 men and 47 women developed new CHD events. In multivariate analysis, the hazard ratio of CHD was approximately two-fold greater in men in the upper tertile of plasma Lp(a) levels, relative to those in the bottom tertile (P < 0.002). The apo(a) isoform size contributed only modestly to the association between Lp(a) and CHD and was not an independent predictor of CHD. In multivariate analysis, Lp(a) cholesterol was not significantly associated with CHD risk in men. In women, no association between Lp(a) and CHD risk was observed. Elevated plasma Lp(a) levels are a significant and independent predictor of CHD risk in men. The assessment of apo(a) isoform size in this cohort does not add significant information about CHD risk. In addition, the cholesterol content in Lp(a) is not a significant predictor of CHD risk.

Lipoprotein a: where are we now?

PURPOSE OF REVIEW

To provide an update of the literature describing the link between lipoprotein a and vascular disease.

RECENT FINDINGS

There is evidence that elevated plasma lipoprotein a levels are associated with coronary heart disease, stroke and other manifestations of atherosclerosis. Several mechanisms may be implicated, including proinflammatory actions and impaired fibrinolysis.

SUMMARY

Lipoprotein a potentially represents a useful tool for risk stratification in the primary and secondary prevention setting. However, there are still unresolved methodological issues regarding the measurement of lipoprotein a levels. Targeting lipoprotein a in order to reduce vascular risk is hampered by the lack of well tolerated and effective pharmacological interventions. Moreover, it has not yet been established whether such a reduction will result in fewer vascular events. The risk attributed to lipoprotein a may be reduced by aggressively tackling other vascular risk factors, such as low-density lipoprotein cholesterol.

All-cause mortality and competing risks of fatal and nonfatal vascular events in the Italian longitudinal study on aging: impact of lipoprotein(a)

Among possible determinants of vascular events, the role of high lipoprotein(a) (Lp[a]) serum levels represents a still uncertain independent risk factor in elderly populations. Moreover, the cumulative incidence of nonfatal vascular events due to high Lp(a) serum levels is conditioned by the competing risk of death from any causes that are a function of age. After a 6.3-year median follow up, we tested the competing risks of all-cause mortality, cumulative fatal-nonfatal stroke events, cumulative fatal-nonfatal coronary artery disease (CAD) events, and nonfatal stroke or CAD events due to high Lp(a) serum levels in a population-based, prospective study conducted in one of the eight centers of the Italian Longitudinal Study on Aging (ILSA), Casamassima, Bari, Italy. Of 704 elderly individuals (65-84 years), 372 (169 women and 203 men) agreed to participate in the study. As compared with those in the lowest Lp(a) tertile serum levels, subjects in the highest tertile (>20 mg/dL) had a higher partially adjusted risk of nonfatal CAD (hazard ratio, 4.19; 95% confidence interval [CI], 1.36-12.94) and nonfatal stroke (hazard ratio, 3.38; 95% CI, 1.00-11.56). Compared with those in the lowest tertile, subjects in the highest tertile had a higher fully adjusted risk of nonfatal CAD (hazard ratio, 3.41; 95% CI, 1.08-10.78). Finally, overall no statistically significant association was found between Lp(a) and the risk of all-cause mortality, cumulative fatal-nonfatal stroke, and cumulative fatal-nonfatal CAD events. In our population, Lp(a) was not a significant independent predictor of stroke and death from all causes, but it was an independent predictor of nonfatal CAD. Finally competing risk, conditioning the timing and occurrence of vascular events in our study population, could be a correct approach for evaluating the role of Lp(a) lipoprotein in vascular disease among elderly people.

Lipoprotein(a) and ischemic heart disease--a causal association? A review

The aim of this review is to summarize present evidence of a causal association of lipoprotein(a) with risk of ischemic heart disease (IHD). Evidence for causality includes reproducible associations of a proposed risk factor with risk of disease in epidemiological studies, evidence from in vitro and animal studies in support of pathophysiological effects of the risk factor, and preferably evidence from randomized clinical trials documenting reduced morbidity in response to interventions targeting the risk factor. Elevated and in particular extreme lipoprotein(a) levels have in prospective studies repeatedly been associated with increased risk of IHD, although results from early studies are inconsistent. Data from in vitro and animal studies implicate lipoprotein(a), consisting of a low density lipoprotein particle covalently bound to the plasminogen-like glycoprotein apolipoprotein(a), in both atherosclerosis and thrombosis, including accumulation of lipoprotein(a) in atherosclerotic plaques and attenuation of t-PA mediated plasminogen activation. No randomized clinical trial of the effect of lowering lipoprotein(a) levels on IHD prevention has ever been conducted. Lacking evidence from randomized clinical trials, genetic studies, such as Mendelian randomization studies, can also support claims of causality. Levels of lipoprotein(a) are primarily determined by variation in the LPA gene coding for the apolipoprotein(a) moiety of lipoprotein(a), and genetic epidemiologic studies have documented association of LPA copy number variants, influencing levels of lipoprotein(a), with risk of IHD. In conclusion, results from epidemiologic, in vitro, animal, and genetic epidemiologic studies support a causal association of lipoprotein(a) with risk of IHD, while results from randomized clinical trials are presently lacking.

Relationship of oxidized phospholipids on apolipoprotein B-100 particles to race/ethnicity, apolipoprotein(a) isoform size, and cardiovascular risk factors: results from the Dallas Heart Study

BACKGROUND

Elevated levels of oxidized phospholipids (OxPLs) on apolipoprotein B-100 particles (OxPL/apoB) are associated with cardiovascular disease and predict new cardiovascular events. Elevated lipoprotein (a) [Lp(a)] levels are a risk factor for cardiovascular disease in whites and also in blacks if they carry small apolipoprotein(a) [apo(a)] isoforms. The relationship of OxPL/apoB levels to race/ethnicity, cardiovascular risk factors, and apo(a) isoforms is not established.

METHODS AND RESULTS

OxPL/apoB levels were measured in 3481 subjects (1831 black, 1047 white, and 603 Hispanic subjects) in the Dallas Heart Study and correlated with age, sex, cardiovascular risk factors, and Lp(a) and apo(a) isoforms. Significant differences in OxPL/apoB levels were noted among racial/ethnic subgroups, with blacks having the highest levels compared with whites and Hispanics (P<0.001 for each comparison). OxPL/apoB levels generally did not correlate with age, sex, or risk factors. In the overall cohort, OxPL/apoB levels strongly correlated with Lp(a) (r=0.85, P<0.001), with the shape of the relationship demonstrating a "reverse L" shape for log-transformed values. The highest correlation was present in blacks, followed by whites and Hispanics; was dependent on apo(a) isoform size; and became progressively weaker with larger isoforms. The size of the major apo(a) isoform (number of kringle type IV repeats) was negatively associated with OxPL/apoB (r=-0.49, P<0.001) and Lp(a) (r=-0.61, P<0.001) regardless of racial/ethnic group. After adjustment for apo(a) isoform size, the relationship between OxPL/apoB and Lp(a) remained significant (r=0.67, P<0.001).

CONCLUSIONS

OxPL/apoB levels vary according to race/ethnicity, are largely independent of cardiovascular risk factors, and are inversely associated with apo(a) isoform size. The association of OxPL with small apo(a) isoforms, in which a similar relationship is present among all racial/ethnic subgroups despite differences in Lp(a) levels, may be a key determinant of cardiovascular risk.

The apolipoprotein(a) gene: linkage disequilibria at three loci differs in African Americans and Caucasians

Lipoprotein(a) (Lp(a)) is an independent, genetically regulated cardiovascular risk factor. Lp(a) plasma levels are largely determined by the apolipoprotein(a) (apo(a)) component, and differ across ethnicity. Although a number of polymorphisms in the apo(a) gene have been identified, apo(a) genetic regulation is not fully understood. To study the relation between apo(a) gene variants, we constructed haplotypes and assessed linkage equilibrium in African Americans and Caucasians for three widely studied apo(a) gene polymorphisms (apo(a) size, +93 C/T and pentanucleotide repeat region (PNR)). Apo(a) size allele frequency distributions were different across ethnicity (p<0.01). For African Americans, PNR frequencies were similar across apo(a) sizes, suggesting linkage equilibrium. For Caucasians, the PNR and the PNR-C/T haplotype frequencies differed for large and small apo(a), with the T and PNR 9 alleles associated with large apo(a) size (p<0.0002); also, the PNR 9 allele was more common on a T allele, while PNR 8 was more common on a C allele. On a C allele background, small PNR alleles were more common and the PNR 10 allele less common among African Americans than Caucasians (p<0.001). The ethnic difference in apo(a) size distribution remained controlling for C/T and PNR alleles (p=0.023). In conclusion, allele and haplotype frequencies and the nature of the linkage disequilibrium differed between African Americans and Caucasians at three apo(a) gene polymorphisms.

Cholesterol Profile Measurement by Vertical Auto Profile Method

Vertical auto profile (VAP) method is a direct single test for measuring comprehensive lipoprotein cholesterol profile. It is based on a well-established method of ultracentrifugation that uses vertical rotor and single density gradient spin. VAP provides cholesterol concentrations of total lipoprotein, high-density lipoprotein (HDL), low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), lipoprotein(a) (Lp(a)), intermediate-density lipoprotein (IDL), HDL subclasses (HDL2 and HDL3), LDL subclasses (LDL1, LDL2, LDL3, and LDL4), VLDL subclasses (VLDL1, VLDL2, and VLDL3), and LDL maximum time, which is directly proportional to LDL size. Because VAP measures additional lipoprotein classes, such as Lp(a), IDL, and subclasses of HDL, LDL, and VLDL, it can identify patients at high risk for coronary heart disease who cannot be identified using the standard lipid panel. In addition, the VAP method is compliant with the National Cholesterol Education Program's Adult Treatment Panel III guidelines.

Ethnicity and lipoprotein(a) polymorphism in Native Mexican populations

BACKGROUND

Lp(a) is a lipoparticle of unknown function mainly present in primates and humans. It consists of a low-density lipoprotein and apo(a), a polymorphic glycoprotein. Apo(a) shares sequence homology and fibrin binding with plasminogen, inhibiting its fibrinolytic properties. Lp(a) is considered a link between atherosclerosis and thrombosis. Marked inter-ethnic differences in Lp(a) concentration related to the genetic polymorphism of apo(a) have been reported in several populations.

AIM

The study examined the structural and functional features of Lp(a) in three Native Mexican populations (Mayos, Mazahuas and Mayas) and in Mestizo subjects.

METHODS

We determined the plasma concentration of Lp(a) by immunonephelometry, apo(a) isoforms by Western blot, Lp(a) fibrin binding by immuno-enzymatic assay and short tandem repeat (STR) polymorphic marker genetic analysis by capillary electrophoresis.

RESULTS

Mestizos presented the less skewed distribution and the highest median Lp(a) concentration (13.25 mg dL(-1)) relative to Mazahuas (8.2 mg dL(-1)), Mayas (8.25 mg dL(-1)) and Mayos (6.5 mg dL(-1)). Phenotype distribution was different in Mayas and Mazahuas as compared with the Mestizo group. The higher Lp(a) fibrin-binding capacity was found in the Maya population. There was an inverse relationship between the size of apo(a) polymorphs and both Lp(a) levels and Lp(a) fibrin binding.

CONCLUSION

There is evidence of significative differences in Lp(a) plasma concentration and phenotype distribution in the Native Mexican and the Mestizo group.

Apo[a] size and PNR explain African American-Caucasian differences in allele-specific apo[a] levels for small but not large apo[a]

Apolipoprotein [a] (apo[a]) gene size is a major predictor of lipoprotein [a] level. To determine genetic predictors of allele-specific apo[a] levels beyond gene size, we evaluated the upstream C/T and pentanucleotide repeat (PNR) polymorphisms. We determined apo[a] sizes, allele-specific apo[a] levels, and C/T and PNR in 215 Caucasians and 139 African Americans. For Caucasians, apo[a] size affected allele-specific levels substantially greater in subjects with apo[a] < 24 K4; for African Americans, the size effect was smaller than in Caucasians, <24 K4, but did not decrease at higher repeats. In both groups, the level decreased with increasing size of the other allele. Controlling for apo[a] sizes, PNR decreased allele-specific apo[a] levels in Caucasians with increasing PNR > 8. In a multiple regression model, apo[a] allele size and size and expression of the other apo[a] allele (and PNR > 8 for Caucasians) significantly predicted allele-specific apo[a] levels. For a common PNR 8 allele, predicted values were similar in the two ethnicities for small size apo[a]. Allele-specific apo[a] levels were influenced by the other allele size and expression. Observed differences between Caucasians and African Americans in allele-specific apo[a] levels were explained for small apo[a] sizes by the other allele size and PNR; the ethnicity differences remain unexplained for larger sizes.

Genetics of the Lp(a)/apo(a) system in an autochthonous Black African population from the Gabon

Plasma lipoprotein(a) (Lp(a)) is a quantitative trait associated with atherothrombotic disease in European and Asian populations. Lp(a) concentrations vary widely within and between populations, with Africans exhibiting on average two- to threefold higher Lp(a) levels and a different distribution compared to Europeans. The apo(a) gene locus on chromosome 6q26-27 (LPA, MIM 152200) has been identified as the major quantitative trait locus (QTL) for Lp(a) concentrations in Europeans and populations of African descent (North American and South African Blacks) but data on autochthonous Black Africans are lacking.Here, we have analysed Lp(a) plasma concentrations, apo(a) isoforms in plasma and four polymorphisms in the LPA gene in 31 African families with 54 children from Gabon. Weighted midparent-offspring regression estimated a heritability h2=0.76. The correlation of Lp(a) levels associated with LPA alleles identical by descent (IBD) resulted in a heritability estimate of 0.801. Our data demonstrate that Lp(a) concentrations are highly heritable in a Central African population without admixture and high Lp(a) (median 43 mg/dl). LPA is the major QTL, explaining most or all of the heritability of Lp(a) in this population.

Significance of apolipoprotein(a) phenotypes in acute coronary syndromes: relation with clinical presentation

BACKGROUND

High lipoprotein(a) [Lp(a)] levels and small-sized apolipoprotein(a) [apo(a)] phenotypes have been linked to acute coronary syndromes (ACS). We sought to determine whether Lp(a) concentrations and apo(a) phenotypes may be related to the clinical syndrome of presentation among ACS patients.

METHODS

Two hundred ten ACS patients and 105 controls were enrolled. One hundred thirteen patients presented with acute myocardial infarction (AMI) and 97 with unstable angina pectoris (UAP). Lp(a) concentrations were determined by ELISA and apo(a) isoforms were detected with a high-resolution immunoblotting method.

RESULTS

Lp(a) levels and the percentage of subjects with at least one small-sized apo(a) isoform were significantly higher both in AMI patients and in UAP subjects as compared with controls. Among ACS patients, the percentage of subjects with at least one small apo(a) phenotype was significantly higher in patients who presented with AMI than in those with UAP (p<0.001). Multivariate logistic regression analysis showed that the presence of at least one small-sized apo(a) isoform was associated with AMI as the patient's clinical syndrome of presentation (OR=2.51, 95% CI: 1.38-4.58, p<0.01).

CONCLUSIONS

Among ACS patients, apo(a) isoforms of low molecular weight were associated with AMI onset. High-resolution apo(a) phenotyping might be helpful to identify individuals at high risk for developing AMI.

Lipoprotein(a): an elusive cardiovascular risk factor

Lipoprotein (a) [Lp(a)], is present only in humans, Old World nonhuman primates, and the European hedgehog. Lp(a) has many properties in common with low-density lipoprotein (LDL) but contains a unique protein, apo(a), which is structurally different from other apolipoproteins. The size of the apo(a) gene is highly variable, resulting in the protein molecular weight ranging from 300 to 800 kDa; this large variation may be caused by neutral evolution in the absence of any selection advantage. Apo(a) influences to a major extent metabolic and physicochemical properties of Lp(a), and the size polymorphism of the apo(a) gene contributes to the pronounced heterogeneity of Lp(a). There is an inverse relationship between apo(a) size and Lp(a) levels; however, this pattern is complex. For a given apo(a) size, there is a considerable variation in Lp(a) levels across individuals, underscoring the importance to assess allele-specific Lp(a) levels. Further, Lp(a) levels differ between populations, and blacks have generally higher levels than Asians and whites, adjusting for apo(a) sizes. In addition to the apo(a) size polymorphism, an upstream pentanucleotide repeat (TTTTA(n)) affects Lp(a) levels. Several meta-analyses have provided support for an association between Lp(a) and coronary artery disease, and the levels of Lp(a) carried in particles with smaller size apo(a) isoforms are associated with cardiovascular disease or with preclinical vascular changes. Further, there is an interaction between Lp(a) and other risk factors for cardiovascular disease. The physiological role of Lp(a) is unknown, although a majority of studies implicate Lp(a) as a risk factor.

A common nonsense mutation in the repetitive Kringle IV-2 domain of human apolipoprotein(a) results in a truncated protein and low plasma Lp(a)

LPA, the gene coding for apolipoprotein(a) [apo(a)], is the major determinant of lipoprotein(a) [Lp(a)] plasma levels, which are associated with risk for coronary heart disease (CHD) and stroke. It is not completely understood how variation in LPA relates to Lp(a) concentrations. One type of variation related to Lp(a) levels is the number of Kringle (K) IV-2 (g.61C>T; GenBank L14005.1) repeats in LPA, but sequence variation may also contribute. Human apo(a) contains from two to >40 nearly identical K IV-2 repeats of genomic size 5.5 kb, which makes it difficult to detect mutations. To elucidate the genetic variation of the apo(a) K IV-2 domain, we isolated a single "nonexpressing" apo(a) allele with 26 K IV-2 repeats, followed by PCR, cloning and sequencing of 96 clones, resulting in an average coverage of each K IV-2 repeat of approximately four-fold. The previously described K IV types 2A and 2B (K IV-2A and K IV-2B) were detected in 74% of the clones. In addition, a new type designated 2C (K IV-2C) was present. A nonsense mutation in the first exon of K IV-2 (g.61C>T) predicted to result in a truncated protein (p.R21X) was found in nine clones on a K IV-2A background. The presence of this mutation was confirmed by analysis of genomic DNA and was shown to represent the rare allele (frequency 0.02) of a SNP. Immunoblot analysis of apo(a) from plasma confirmed the presence of a truncated apo(a) isoform in the index individual and family members. Our data show that SNPs affecting Lp(a) plasma concentrations also exist in the apo(a) K IV-2 domain.

[New aspects of normolipidemic dyslipoproteinemias]

INTRODUCTION

Normolipidemic dislipoproteinemias include various disorders of different lipoproteins, of their subfractions or some apolipo-proteins, of primary or secondary origin, which are widespread among general population and, like hyperlipoproteinemias, they are associated with the risk for premature atherosclerosis.

DECREASED LEVEL OF HDL CHOLESTEROL

It is a primary, familial hypoalphalipoproteinemia, which is commonly associated with obesity, diet rich in carbohydrates, decreased physical activity and excessive use of coffee and some drugs.

HYPERAPOBETALIPOPROTEINEMIA

It is characterized by increase of apo B-100 in LDL particles, most probably as a consequence of increased hepatic synthesis. Apolipoprotein E isoforms ApoE4 isoform is associated with elevated LDL-cholesterol concentration due to rapid IDL to LDL conversion.

ELECTROPHORETIC DISORDERS

The most important is the latent type IV (pre-beta) or IVb (pre-beta1) with decreased VLDL clearance.

PROLONGED POSTPRANDIAL LIPEMIA

It is common in obesity, NIDDM and coronary heart disease, as an independent risk factor for premature atherosclerosis.

INCREASED OXIDATIVE MODIFICATION OF THE LDL AND HDL PARTICLES

Oxidatively modified LDL may have a key role in the pathogenesis of atherosclerosis and oxidative modification of HDL reduces its transport capacity and its inhibition of LDL oxidation. INCREASED LEVEL OF LP(A) Lp(a) is an independent risk factor for premature atherosclerosis, primarily in young and middle-aged men, in persons with elevated global cardiovascular risk factor profile, decreased HDL-cholesterol, and hypertension. The risk is smaller in persons taking hypocholesterolemic drugs. Also, it is elevated in NIDDM, hypothyroidism and kidney disease.