Monogenic dyslipidemias: window on determinants of plasma lipoprotein metabolism

Hypertriglyceridemia Results From an Impaired Catabolism of Triglyceride-Rich Lipoproteins in PLIN1-Related Lipodystrophy

BACKGROUND

Pathogenic variants in PLIN1-encoding PLIN1 (perilipin-1) are responsible for an autosomal dominant form of familial partial lipodystrophy (FPL) associated with severe insulin resistance, hepatic steatosis, and important hypertriglyceridemia. This study aims to decipher the mechanisms of hypertriglyceridemia associated with PLIN1-related FPL.

METHODS

We performed an in vivo lipoprotein kinetic study in 6 affected patients compared with 13 healthy controls and 8 patients with type 2 diabetes. Glucose and lipid parameters, including plasma LPL (lipoprotein lipase) mass, were measured. LPL mRNA and protein expression were evaluated in abdominal subcutaneous adipose tissue from patients with 5 PLIN1-mutated FPL and 3 controls.

RESULTS

Patients with PLIN1-mutated FPL presented with decreased fat mass, insulin resistance, and diabetes (glycated hemoglobin A1c, 6.68±0.70% versus 7.48±1.63% in patients with type 2 diabetes; mean±SD; P=0.27). Their plasma triglycerides were higher (5.96±3.08 mmol/L) than in controls (0.76±0.27 mmol/L; P<0.0001) and patients with type 2 diabetes (2.94±1.46 mmol/L, P=0.006). Compared with controls, patients with PLIN1-related FPL had a significant reduction of the indirect fractional catabolic rate of VLDL (very-low-density lipoprotein)-apoB100 toward IDL (intermediate-density lipoprotein)/LDL (low-density lipoprotein; 1.79±1.38 versus 5.34±2.45 pool/d; P=0.003) and the indirect fractional catabolic rate of IDL-apoB100 toward LDL (2.14±1.44 versus 7.51±4.07 pool/d; P=0.005). VLDL-apoB100 production was not different between patients with PLIN1-related FPL and controls. Compared with patients with type 2 diabetes, patients with PLIN1-related FPL also showed a significant reduction of the catabolism of both VLDL-apoB100 (P=0.031) and IDL-apoB100 (P=0.031). Plasma LPL mass was significantly lower in patients with PLIN1-related FPL than in controls (21.03±10.08 versus 55.76±13.10 ng/mL; P<0.0001), although the LPL protein expression in adipose tissue was similar. VLDL-apoB100 and IDL-apoB100 indirect fractional catabolic rates were negatively correlated with plasma triglycerides and positively correlated with LPL mass.

CONCLUSIONS

We show that hypertriglyceridemia associated with PLIN1-related FPL results from a marked decrease in the catabolism of triglyceride-rich lipoproteins (VLDL and IDL). This could be due to a pronounced reduction in LPL availability, related to the decreased adipose tissue mass.

Helicobacter pylori promotes gastric cancer through CagA-mediated mitochondrial cholesterol accumulation by targeting CYP11A1 redistribution

Cholesterol and Helicobacter pylori (H. pylori) are both risk factors for gastric cancer (GC). However, the relationship between cholesterol and H. pylori and their function in the progression of GC are controversial. In this study, we addressed that H. pylori could induce mitochondrial cholesterol accumulation and promote GC proliferation and protect GC cells against apoptosis via cholesterol. Metabolomic and transcriptomic sequencing were used to identify CYP11A1 responsible for H. pylori-induced cholesterol accumulation. In vitro and in vivo function experiments revealed that cholesterol could promote the proliferation of GC and inhibit apoptosis. Mechanically, the interaction of Cytotoxin-associated gene A (CagA) and CYP11A1 redistributed mitochondrial CYP11A1 outside the mitochondria and subsequently caused mitochondrial cholesterol accumulation. The CYP11A1-knockdown upregulated cholesterol accumulation and reproduced the effect of cholesterol on GC in a cholesterol-dependent manner. Moreover, CYP11A1-knockdown or H. pylori infection inhibited mitophagy and maintained the mitochondria homeostasis. H. pylori could contribute to the progression of GC through the CagA/CYP11A1-mitoCHO axis. This study demonstrates that H. pylori can contribute to the progression of GC via cholesterol, and eradicating H. pylori is still prognostically beneficial to GC patients.

SEA 2024 Standards for Global Control of Vascular Risk

One of the objectives of the Spanish Society of Arteriosclerosis is to contribute to the knowledge, prevention and treatment of vascular diseases, which are the leading cause of death in Spain and entail a high degree of disability and health expenditure. Atherosclerosis is a multifactorial disease and its prevention requires a global approach that takes into account the associated risk factors. This document summarises the current evidence and includes recommendations for patients with established vascular disease or at high vascular risk: it reviews the symptoms and signs to evaluate, the laboratory and imaging procedures to request routinely or in special situations, and includes the estimation of vascular risk, diagnostic criteria for entities that are vascular risk factors, and general and specific recommendations for their treatment. Finally, it presents aspects that are not usually referenced in the literature, such as the organisation of a vascular risk consultation.

Acute pancreatitis secondary to moderate hypertriglyceridemia: A case report

Key Clinical Message

It is crucial to remain vigilant about acute pancreatitis, even in cases with moderately elevated triglycerides. Triglycerides as a cause of acute pancreatitis must be considered even in the absence of other risk factors.

Abstract

Hypertriglyceridemia is one of the most common causes of acute pancreatitis (AP), with triglyceride levels greater than 1000 mg/dL being an established risk factor for AP. Cases of acute pancreatitis due to triglyceride levels less than 1000 mg/dL have rarely been reported in the literature. We report a case of a 26-year-old para-2, living-2 (P2L2) female who presented with epigastric pain and fever, with a serum triglyceride level of 579 mg/dL. A diagnosis of acute pancreatitis was made based on the clinical features and radiological findings, despite no identifiable risk factors. Hypertriglyceridemia was managed with no complications of acute pancreatitis during treatment.

Recurrent pancreatitis secondary to hypertriglyceridemia: A case report and case review

Key Clinical Message

Managing acute pancreatitis secondary to hypertriglyceridemia in pregnancy is challenging. The use of intravenous insulin along with lipid lowering drugs can be an option in settings where plasmapharesis and gene therapy are unavailable.

Abstract

Acute pancreatitis secondary to hypertriglyceridemia is rare but various studies have highlighted it as the third most common cause following gallstones and alcohol consumption. Managing acute pancreatitis is always challenging; even more challenging during pregnancy. We present a case of a 31-year- old female with a history of recurrent pancreatitis secondary to hypertriglyceridemia with a current episode of acute pancreatitis at 21 weeks of gestation.

Prevalence of lipoprotein lipase mutation in patients with severe hypertriglyceridemia and the characteristic features of hypertriglyceridemic pancreatitis

Aim: We conducted a retrospective study with the aim of determining the prevalence of lipoprotein lipase (LPL) mutation in patients with severe hypertriglyceridemia (HTG) and to study differences in characteristic features of HTG induced acute pancreatitis (AP). Materials and Methods: Seventy adults with a serum triglyceride (TG) level ≥500 mg/dL were included in the study. Baseline characteristics, LPL mutation and risk factors between those with and without HTG-AP were compared. Results: The mean age was 43 ± 12 years, and males accounted for 55.7%. Of the patients 35 had TG level

SEA 2022 Standards for Global Control of Cardiovascular Risk

One of the objectives of the Spanish Society of Arteriosclerosis is to contribute to better knowledge of vascular disease, its prevention and treatment. It is well known that cardiovascular diseases are the leading cause of death in our country and entail a high degree of disability and health care costs. Arteriosclerosis is a multifactorial disease and therefore its prevention requires a global approach that takes into account the different risk factors with which it is associated. Therefore, this document summarizes the current level of knowledge and includes recommendations and procedures to be followed in patients with established cardiovascular disease or at high vascular risk. Specifically, this document reviews the main symptoms and signs to be evaluated during the clinical visit, the laboratory and imaging procedures to be routinely requested or requested for those in special situations. It also includes vascular risk estimation, the diagnostic criteria of the different entities that are cardiovascular risk factors, and makes general and specific recommendations for the treatment of the different cardiovascular risk factors and their final objectives. Finally, the document includes aspects that are not usually referenced in the literature, such as the organization of a vascular risk consultation.

Standards for global cardiovascular risk management arteriosclerosis

One of the main goals of the Spanish Society of Arteriosclerosis is to contribute to a wider and greater knowledge of vascular disease, its prevention and treatment. Cardiovascular diseases are the leading cause of death in our country and also lead to a high degree of disability and health expenditure. Arteriosclerosis is a multifactorial disease, this is why its prevention requires a global approach that takes into account the different risk factors with which it is associated. Thus, this document summarizes the current level of knowledge and integrates recommendations and procedures to be followed for patients with established cardiovascular disease or high vascular risk. Specifically, this document reviews the main symptoms and signs to be evaluated during the clinical visit, the laboratory and imaging procedures to be routinely requested or those in special situations. It also includes the estimation of vascular risk, the diagnostic criteria of the different entities that are cardiovascular risk factors, and presents general and specific recommendations for the treatment of the different cardiovascular risk factors and their final objectives. Finally, the document includes aspects that are not often mentioned in the literature, such as the organisation of a vascular risk consultation.

Artemisia Iwayomogi Extract Attenuates High-Fat Diet-Induced Hypertriglyceridemia in Mice: Potential Involvement of the Adiponectin-AMPK Pathway and Very Low Density Lipoprotein Assembly in the Liver

This study aimed to examine the protective effect of Artemisia iwayomogi extract (AI) against hypertriglyceridemia induced by a high-fat diet (HFD) in mice and to uncover the underlying molecular mechanisms. C57BL/6N mice were fed chow, HFD, HFD + 0.1% AI, HFD + 0.25% AI, or HFD + 0.5% AI for 10 weeks. The addition of 0.25% and 0.5% AI resulted in dose-dependent improvements in the major parameters of hypertriglyceridemia, including plasma triglyceride, free fatty acids, apolipoprotein B, and lipoprotein lipase, with parallel reductions in body weight gain, hepatic lipid accumulation, and insulin resistance. These beneficial effects were accompanied by the activation of adiponectin-adenosine monophosphate-activated protein kinase (AMPK) mediated signaling cascades in the liver, which downregulated molecules involved in lipogenesis and concurrently upregulated molecules related to fatty acid oxidation. The downregulation of molecules involved in very low density lipoprotein assembly, which was associated with improved hepatic insulin signaling, also appeared to contribute to the AI-induced attenuation of hypertriglyceridemia.

Systems biology of personalized nutrition

Personalized nutrition is fast becoming a reality due to a number of technological, scientific, and societal developments that complement and extend current public health nutrition recommendations. Personalized nutrition tailors dietary recommendations to specific biological requirements on the basis of a person's health status and goals. The biology underpinning these recommendations is complex, and thus any recommendations must account for multiple biological processes and subprocesses occurring in various tissues and must be formed with an appreciation for how these processes interact with dietary nutrients and environmental factors. Therefore, a systems biology-based approach that considers the most relevant interacting biological mechanisms is necessary to formulate the best recommendations to help people meet their wellness goals. Here, the concept of "systems flexibility" is introduced to personalized nutrition biology. Systems flexibility allows the real-time evaluation of metabolism and other processes that maintain homeostasis following an environmental challenge, thereby enabling the formulation of personalized recommendations. Examples in the area of macro- and micronutrients are reviewed. Genetic variations and performance goals are integrated into this systems approach to provide a strategy for a balanced evaluation and an introduction to personalized nutrition. Finally, modeling approaches that combine personalized diagnosis and nutritional intervention into practice are reviewed.

Efficacy and Safety of Lomitapide in Japanese Patients with Homozygous Familial Hypercholesterolemia

Aim: There is an unmet need in Japan for more optimal lipid-lowering therapy (LLT) for patients with homozygous familial hypercholesterolemia (HoFH) who respond inadequately to available drug therapies and/or apheresis, to achieve goals of low-density lipoprotein cholesterol (LDL-C) reduction by 50% or to < 100 mg/dL.

Methods: In this study, Japanese patients with HoFH on stable LLT and diet were treated with lomitapide, initiated at 5 mg/day and escalated to maximum tolerated dose (up to 60 mg/day) over 14 weeks. The primary efficacy endpoint was mean percentage change from baseline to Week 26 in LDL-C. Secondary endpoints included changes in other lipid parameters and safety throughout the 56-week study (including follow-up).

Results: Nine patients entered the efficacy phase of the study and, of these, eight completed 56 weeks. Mean LDL-C was reduced by 42% (p < 0.0001) at 26 weeks, from 199 mg/dL (95% CI: 149–250) at baseline to 118 mg/dL (95% CI: 70–166). A 50% reduction in LDL-C and LDL-C < 100 mg/dL was achieved by five and six of nine patients, respectively, at 26 weeks. After 56 weeks, LDL-C was reduced by 38% (p = 0.0032) from baseline. Significant reductions in non-HDL-C, VLDL-C, triglycerides, and apolipoprotein B were also reported at Week 26. There were no new safety signals and, similar to previous studies, gastrointestinal adverse events were the most common adverse events.

Conclusion: Lomitapide, added to ongoing treatment with other LLTs, was effective in rapidly and significantly reducing the levels of LDL-C and other atherogenic apolipoprotein B-containing lipoproteins in adult Japanese patients with HoFH.

Targeting microsomal triglyceride transfer protein and lipoprotein assembly to treat homozygous familial hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) is a polygenic disease arising from defects in the clearance of plasma low-density lipoprotein (LDL), which results in extremely elevated plasma LDL cholesterol (LDL-C) and increased risk of atherosclerosis, coronary heart disease, and premature death. Conventional lipid-lowering therapies, such as statins and ezetimibe, are ineffective at lowering plasma cholesterol to safe levels in these patients. Other therapeutic options, such as LDL apheresis and liver transplantation, are inconvenient, costly, and not readily available. Recently, lomitapide was approved by the Federal Drug Administration as an adjunct therapy for the treatment of HoFH. Lomitapide inhibits microsomal triglyceride transfer protein (MTP), reduces lipoprotein assembly and secretion, and lowers plasma cholesterol levels by over 50%. Here, we explain the steps involved in lipoprotein assembly, summarize the role of MTP in lipoprotein assembly, explore the clinical and molecular basis of HoFH, and review pre-clinical studies and clinical trials with lomitapide and other MTP inhibitors for the treatment of HoFH. In addition, ongoing research and new approaches underway for better treatment modalities are discussed.

Genetic predisposition of human plasma triglyceride concentrations

The issue of plasma triglyceride levels relative to the risk of development of cardiovascular disease, as well as overall mortality, has been actively discussed for many years. Like other cardiovascular disease risk factors, final plasma TG values have environmental influences (primarily dietary habits, physical activity, and smoking), and a genetic predisposition. Rare mutations (mainly in the lipoprotein lipase and apolipoprotein C2) along with common polymorphisms (within apolipoprotein A5, glucokinase regulatory protein, apolipoprotein B, apolipo-protein E, cAMP responsive element binding protein 3-like 3, glycosylphosphatidylinositol-anchored HDL-binding protein 1) play an important role in determining plasma TG levels.

Review: Genetics of the cardiometabolic syndrome: new insights and therapeutic implications

Although the definition of the phenotype is imprecise, cardiometabolic syndrome (CMS) includes a constellation of complex diseases such as type 2 diabetes, dislipidemias, central obesity and hypertension, proinflammatory and prothrombotic states, ovarian polycystosis and fatty liver. The genetics of each disease is complex in itself and varies in spectrum from monogenic and syndromic models of inheritance, usually rare, to the most common polygenic and multifactorial forms. In addition, human studies using the candidate-gene approach indicate that common genetic variants of several genes are associated with the development of CMS. Genome-wide scans have also provided several chromosomal regions associated with some of the components of CMS. In addition, through comparative genomics animal models can generate a map for candidate loci in humans and a promising approach is offered by bioinformatic tools for gene prioritization. Lastly, the involvement of genes whose products are already the targets for approved drugs, such as SLC6A4, PPARα and PPARγ , in the development of CMS suggests new avenues for CMS pharmacological treatment.

Remnant Lipoprotein Cholesterol and Incident Coronary Heart Disease: The Jackson Heart and Framingham Offspring Cohort Studies

Background

Remnant lipoproteins (RLPs), the triglyceride‐enriched precursors to low‐density lipoprotein, are an emerging risk factor for coronary heart disease (CHD). We sought to determine the association of RLP cholesterol (RLP‐C) levels with incident CHD in 2 diverse, prospective, longitudinal observational US cohorts.

Methods and Results

We analyzed cholesterol levels from serum lipoprotein samples separated via density gradient ultracentrifugation in 4114 US black participants (mean age 53.8 years, 64% women) from the Jackson Heart Study and a random sample of 818 predominantly white participants (mean age 57.3 years, 52% women) from the Framingham Offspring Cohort Study. Multivariable‐adjusted hazard ratios (HRs) for RLP‐C (the sum of very low‐density lipoprotein₃ cholesterol and intermediate‐density lipoprotein cholesterol) were derived to estimate associations with incident CHD events consisting of myocardial infarction, CHD death, and revascularizations for each cohort separately and as a combined population. There were 146 CHD events in the combined population. After adjustments for age, sex, body mass index, smoking, blood pressure, diabetes, and lipid‐lowering therapy for the combined population, RLP‐C (HR 1.23 per 1‐SD increase, 95% CI 1.06–1.42, P<0.01) and intermediate‐density lipoprotein cholesterol (HR 1.26 per 1‐SD increase, 95% CI 1.08–1.47, P<0.01) predicted CHD during an 8‐year follow‐up. Associations were attenuated by high‐density lipoprotein cholesterol and ultimately lost significance with inclusion of real low‐density lipoprotein cholesterol, which excludes Lp(a) and IDL cholesterol fractions. Similar associations were seen in multivariable analyses within each cohort.

Conclusion

RLP‐C levels are predictive of incident CHD in this diverse group of primary prevention subjects. Interventions aimed at reducing RLP‐C to prevent CHD warrant further intensive investigation.

Clinical Trial Registration

URL: http://www.ClinicalTrials.gov. Unique identifier: NCT00415415.

Effectiveness of omega-3 polysaturated fatty acids (fish oil) supplementation for treating hypertriglyceridemia in children and adolescents

Limited pharmacological options are available for management pediatric hypertriglyceridemia. We examined the effectiveness of dietary fish oil supplementation as a means to reduce triglyceride levels in pediatric patients. We reviewed 111 children aged 8 to 18 years with hypertriglyceridemia (≥1.5 mmol/L) undergoing treatment in a specialized dyslipidemia clinic. At the treating cardiologist's discretion, 60 subjects received nonprescription fish oil supplementation (500-1000 mg/d), while the remaining patients did not. Initially there were no baseline differences between groups, including the use of concomitant lipid-lowering medication. Treatment with fish oil was associated with a potential clinically relevant but non-statistically significant decrease in triglycerides and triglyceride-to-high-density lipoprotein (HDL) ratio. Fish oil had no effect on HDL-cholesterol, non-HDL-cholesterol, or total cholesterol. All associations remained unchanged when adjusted for body mass index z score, nutrition, physical activity, and screen time. Fish oil supplementation was not significantly effective in treating hypertriglyceridemia in pediatric patients.

What We Know About Diet, Genes, and Dyslipidemia: Is There Potential for Translation?

Cardiovascular disease, particularly coronary artery disease (CAD), is the leading cause of death in the United States. Dyslipidemia, including elevated low density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels and low high density lipoprotein cholesterol (HDL-C), is a well-established risk factor for CAD and is influenced by both genetic and lifestyle factors, including the diet and dietary fat in particular. Major strides in elucidating the genetic basis for dyslipidemia have been made in recent years, and the quest to clarify how genetic differences influence lipid response to dietary intervention continues. Some monogenic conditions such as famililal hypercholesterolemia and sitosterolemia already have customized dietary recommendations. Some promising associations have emerged for more polygenic dyslipidemia, but further studies are needed in large dietary intervention studies capturing increasing amounts of explainable genetic variation before recommendations can be made for clinical translation.

The g.-469G>A polymorphism in the GPIHBP1 gene promoter is associated with hypertriglyceridemia and has an additive effect on the risk conferred by LPL defective alleles

BACKGROUND AND AIMS

Hypertriglyceridemia (hyperTG) is a component of the metabolic syndrome and a cardiovascular or pancreatitis risk factor. Although both genetic and environmental factors influence its expression, the biological component of hyperTG is still underestimated and has been reported in 10-20% of cases only. Given its key role in the lipolysis of TG-rich lipoproteins, glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) is a biological candidate for hyperTG. The aim of this study was to assess the association of new GPIHBP1 gene variants with hyperTG (fasting plasma TG values ≥ 2.0 mmol/L).

METHODS AND RESULTS

Sequencing the GPIHBP1 gene identified a g.-469G > A (rs72691625) polymorphism in the promoter. A sample of 541 Caucasians (263 normoTG and 278 hyperTG) was then screened for this polymorphism using a 5'nuclease TaqMan. In multivariate analyses, GPIHBP1 g.-469G > A polymorphism carriers were at significantly higher risk of hyperTG (≥ 2.0 mmol/L) than non-carriers, the odds ratio (OR) being 1.67 (p = 0.025) among heterozygotes and 5.70 (p = 0.004) in homozygotes. The simultaneous presence of loss-of-function LPL polymorphisms had an incremental additive effect on the risk of hyperTG (OR: 7.30; p < 0.001), highlighting the importance of gene-gene interactions in the expression of hyperTG.

CONCLUSIONS

In this study, the g.-469G >A polymorphism in the GPIHBP1 gene promoter was associated with an increased risk of hyperTG and had an additive effect on the risk conferred by LPL defective alleles.

Genetic determinants of lipid homeostasis

Circulating levels of blood lipids are heritable risk factors for atherosclerosis and heart disease, and are the target of therapeutic intervention. Studies of monogenic disorders and - more recently - genome-wide association studies have identified several important genetic determinants of blood lipid levels. These have the potential to provide new drug targets to alter blood lipid levels and may improve prediction of cardiovascular disease. Better functional validation of lipid loci is required to clarify the biological role of proteins encoded by specific genomic regions and understand how they influence lipid metabolism and confer disease risk.

Hypertriglyceridemia-induced recurrent acute pancreatitis: A case-based review

Hypertriglyceridemia is a rare, but well-known cause of acute pancreatitis. A serum triglyceride level of more than 1000 to 2000 mg / dl is the identifiable risk factor. It typically presents as an episode of acute pancreatitis or recurrent acute pancreatitis. The clinical course and routine management of Hypertriglyceridemia-induced pancreatitis is similar to other causes. A thorough family history is important, as is the identification of secondary causes of hypertriglyceridemia. The mainstay of therapy includes dietary restriction of fatty meal and fibric acid derivatives. We hereby report the case of a 37-year-old lady with a family history of dyslipidemia presenting with recurrent episodes of acute pancreatitis. We also review the literature for pathogenesis and management of hyperlipidemia.

The relative importance of common and rare genetic variants in the development of hypertriglyceridemia

Plasma lipid levels are a complex trait with a genetic and an environmental component. There are two models for the genetic basis of complex traits: the common-disease common-variant hypothesis, in which susceptibility is due to variants occurring at relatively high frequency but low effect size; and the common-disease rare-variant hypothesis, where disease is due to multiple rare variants each occurring at low frequency but with high effect size. Genome-wide association studies have identified a number of common variants associated with plasma lipid levels. However, they account for only a proportion of the genetic variance. Resequencing studies are revealing the importance of rare variants in accounting for the missing variance. Next-generation sequencing will allow the relative importance of the two hypotheses to be assessed.

Hypertriglyceridemia: phenomics and genomics

Hypertriglyceridemia is a common complex metabolic trait that is associated with increased atherosclerosis risk, presence of the metabolic syndrome and, with extreme elevation, increased risk of pancreatitis. Hierarchical cluster analysis using clinical and biochemical features of the Frederickson hyperlipoproteinemia types can generate hypotheses for molecular genetic studies. High throughput resequencing of individuals at the extremes of plasma triglyceride concentration has shown that both rare genetic variants with large effects and common genetic variants with moderate effects explain a relatively large proportion of variation. Very recent progress using high-density sets of genome-wide markers have identified additional genetic determinants of plasma triglyceride concentrations, albeit within largely normolipidemic subjects and with small effect sizes. Phenomic evaluation of patients with hypertriglyceridemia might help to clarify genotype-phenotype correlations and responses to interventions.

Monogenic Hypocholesterolaemic Lipid Disorders and Apolipoprotein B Metabolism

The study of apolipoprotein (apo) B metabolism is central to our understanding of human lipoprotein metabolism. Moreover, the assembly and secretion of apoB-containing lipoproteins is a complex process. Increased plasma concentrations of apoB-containing lipoproteins are an important risk factor for the development of atherosclerotic coronary heart disease. In contrast, decreased levels of, but not the absence of, these apoB-containing lipoproteins is associated with resistance to atherosclerosis and potential long life. The study of inherited monogenic dyslipidaemias has been an effective means to elucidate key metabolic steps and biologically relevant mechanisms. Naturally occurring gene mutations in affected families have been useful in identifying important domains of apoB and microsomal triglyceride transfer protein (MTP) governing the metabolism of apoB-containing lipoproteins. Truncation-causing mutations in the APOB gene cause familial hypobetalipoproteinaemia, whereas mutations in MTP result in abetalipoproteinaemia; both rare conditions are characterised by marked hypocholesterolaemia. The purpose of this review is to examine the role of apoB in lipoprotein metabolism and to explore the key biochemical, clinical, metabolic and genetic features of the monogenic hypocholesterolaemic lipid disorders affecting apoB metabolism.

Single nucleotide polymorphisms in the apo(a) kringle IV type 8 domain are not associated with atherothrombotic serum lipoprotein (a) concentration, in a Portuguese paediatric population

Lipoprotein (a) (Lp[a]) is a complex of apolipoprotein (a) (apo[a]) and low-density lipoprotein (LDL), associated with atherothrombotic disease. Most of the interindividual variations in plasma levels of Lp(a) can be attributed to sequence differences linked to the apo(a) gene locus. The aim of this study was to investigate a possible link between single nucleotide polymorphisms (SNPs) in the apo(a) kringle (K) IV type 8 domain and atherothrombotic serum Lp(a) concentrations. Direct sequencing of the two exons and flanking intronic sequences of the apo(a) K IV type 8 domain was performed in a group of 97 paediatric patients, 51 with serum Lp(a) concentration above and 46 with concentration below 30 mg/dl,. We found three SNPs, two in exon 1 (c.66A>C and c.133G>A) and one in intron 1 (c.160+1G>A). The c.66A>C polymorphism was the most common with a heterozygosity frequency of 15.46%. The c.133G>A and c.160+1G>A polymorphisms were found at a frequency of 5.15% and 1.03%, respectively. No statistically significant difference was found in the genotype distribution between the two groups of patients. Our results suggest that these SNPs in the apo(a) K IV 8 domain are not directly associated with atherothrombotic serum Lp(a) concentration in our population.

Advances in pharmacogenomics of antiretrovirals: an update

Recent developments in the pharmacogenomics of antiretroviral drugs provide new prospects for predicting the efficacy of treatment and potential adverse effects. HIV/AIDS is a serious but treatable infectious disease, yet current treatment is limited by high rates of adverse drug reactions and development of resistance due to suboptimal drug concentrations in a significant proportion of patients. Antiretroviral therapy is especially suitable for pharmacogenomic investigation as both drug exposure and treatment response can be quantified and certain adverse effects can be assessed with validated measures. Additionally, there is increasing knowledge of the pharmacokinetics and dynamics of antiretroviral drugs, and some candidate genes implicated in the metabolism, transport and adverse effects have been identified. However, recent studies of the association of particular genes and their genetic variants with HIV management and adverse drug reactions have not provided unifying conclusions. This article reviews the most recently published work and summarizes the state of research in this area. Future directions for research and the application of this technology to the clinical practice of individualizing treatment for HIV management are discussed.

Hypertriglyceridaemia and low plasma HDL in a patient with apolipoprotein A-V deficiency due to a novel mutation in the APOA5 gene

APOA5 encodes a novel apolipoprotein (apo A-V) which appears to be a modulator of plasma triglyceride (TG). In apoA5 knock out mice plasma TG level increases almost fourfold, whereas in human APOA5 transgenic mice it decreases by 70%. Some SNPs in the APOA5 gene have been associated with variations in plasma TG in humans. In addition, hypertriglyceridaemic (HTG) patients have been identified who carried rare nonsense mutations in the APOA5 gene (Q139X and Q148X), predicted to result in apo A-V deficiency. In this study we report a 17-year-old male with high TG and low high density lipoprotein cholesterol (HDL-C), who at the age of two had been found to have severe HTG and eruptive xanthomas suggesting a chylomicronaemia syndrome. Plasma postheparin LPL activity, however, was normal and no mutations were found in LPL and APOC2 genes. The sequence of APOA5 gene revealed that the patient was homozygous for a point mutation (c.289 C>T) in exon 4, converting glutamine codon at position 97 into a termination codon (Q97X). Apo A-V was not detected in patient's plasma, indicating that he had complete apo A-V deficiency. The administration of a low-fat and low-oligosaccharide diet, either alone or supplemented with omega-3 fatty acids, started early in life, reduced plasma TG to a great extent but had a negligible effect on plasma HDL-C. Loss of function mutations of APOA5 gene may be the cause of severe HTG in patients without mutations in LPL and APOC2 genes.

Monogenic pediatric dyslipidemias: classification, genetics and clinical spectrum

Monogenic disorders that cause abnormal levels of plasma cholesterol and triglycerides have received much attention due to their role in metabolic dysfunction and cardiovascular disease. While these disorders often present clinically during adulthood, some present most commonly in the pediatric population and can have serious consequences if misdiagnosed or untreated. This review provides an overview of monogenic lipid disorders that present with unusually high or low levels of plasma cholesterol and/or triglycerides during infancy, childhood and adolescence. Biochemical and genetic findings, clinical presentation and treatment options are discussed with an emphasis upon recent advances in our understanding and management of these monogenic disorders.

Genetic association of low-density lipoprotein receptor-related protein 2 (LRP2) with plasma lipid levels

AIM

Not all genetic factors predisposing phenotypic features of dyslipidemia have been identified. We studied the association between the low density lipoprotein-related protein 2 gene (LRP2) and levels of plasma total cholesterol (T-Cho) and LDL-cholesterol (LDL-C) among 352 adults in Japan.

METHODS

Subjects were obtained from among participants in a cohort study that was carried out with health-check screening in an area of east-central Japan. We selected 352 individuals whose LDL-C levels were higher than 140 mg/dL from the initially screened 22,228 people. We assessed the relation between plasma cholesterol levels and single-nucleotide polymorphisms (SNPs) in the LRP2 gene.

RESULTS

We identified significant correlations between plasma cholesterol levels and two of 19 examined SNPs in LRP2, c.+193826T/C and IVS55 - 147A/G. In particular, the association of c.+193826T/C with the T-Cho level was prominent (p=0.003), showing a co-dominant effect of the minor C-allele on lowering T-Cho and LDL-C levels: for 24 homozygous C-allele carriers, T-Cho=240.7 +/- 24.2 mg/dL and LDL-C=166.1 +/- 21.0 mg/dL); for 130 heterozygous carriers, 248.5 +/- 23.5 mg/dL and 166.6 +/- 19.3 mg/dL; and for 196 homozygous T-allele carriers, 253.9 +/- 23.5 mg/dL and 172.0 +/- 21.0 mg/dL. Linkage disequilibrium (LD) analyses based on 19 selected SNPs showed that c.+193826T/C and IVS55 - 147A/G were in tight LD and that both were located in an LD block covering the genomic sequence from exon 55 to exon 61.

CONCLUSION

We confirm the association between LRP2 and levels of T-Cho and LDL-C in human plasma. The results suggest that genetic variations in LRP2 are important factors affecting lipoprotein phenotypes of patients with hypercholesterolemia.

Identification of a chromosome 8p locus for early-onset coronary heart disease in a French Canadian population

Susceptibility to coronary heart disease (CHD) has long been known to exhibit familial aggregation, with heritability estimated to be greater than 50%. The French Canadian population of the Saguenay-Lac Saint-Jean region of Quebec, Canada is descended from a founder population that settled this region 300-400 years ago and this may provide increased power to detect genes contributing to complex traits such as CHD. Probands with early-onset CHD, defined by angiographically determined coronary stenosis, and their relatives were recruited from this population (average sibship size of 6.4). Linkage analysis was performed following a genome-wide microsatellite marker scan on 42 families with 284 individuals. Nonparametric linkage (NPL) analysis provided suggestive evidence for a CHD susceptibility locus on chromosome 8 with an NPL score of 3.14 (P=0.001) at D8S1106. Linkage to this locus was verified by fine mapping in an enlarged sample of 50 families with 320 individuals. This analysis provided evidence of linkage at D8S552 (NPL score=3.53, P=0.0003), a marker that maps to the same location as D8S1106. Candidate genes in this region, including macrophage scavenger receptor 1, farnesyl-diphosphate farnesyltransferase 1, fibrinogen-like 1, and GATA-binding protein 4, were resequenced in all coding exons in both affected and unaffected individuals. Association studies with variants in these and five other genes did not identify a disease-associated mutation. In conclusion, a genome-wide scan and additional fine mapping provide evidence for a locus on chromosome 8 that contributes to CHD in a French Canadian population.

Missense mutations in APOB within the betaalpha1 domain of human APOB-100 result in impaired secretion of ApoB and ApoB-containing lipoproteins in familial hypobetalipoproteinemia

Familial hypobetalipoproteinemia (FHBL) is associated with mutations in the APOB gene. We reported the first missense APOB mutation, R463W, in an FHBL kindred (Burnett, J. R., Shan, J., Miskie, B. A., Whitfield, A. J., Yuan, J., Tran, K., Mc-Knight, C. J., Hegele, R. A., and Yao, Z. (2003) J. Biol. Chem. 278, 13442-13452). Here we identified a second nonsynonymous APOB mutation, L343V, in another FHBL kindred. Heterozygotes for L343V (n = 10) had a mean plasma apoB at 0.31 g/liter as compared with 0.80 g/liter in unaffected family members (n = 22). The L343V mutation impaired secretion of apoB-100 and very low density lipoproteins. The secretion efficiency was 20% for B100wt and 10% for B100LV and B100RW. Decreased secretion of mutant apoB-100 was associated with increased endoplasmic reticulum retention and increased binding to microsomal triglyceride transfer protein and BiP. Reduced secretion efficiency was also observed with B48LV and B17LV. Biochemical and biophysical analyses of apoB domain constructs showed that L343V and R463W altered folding of the alpha-helical domain within the N terminus of apoB. Thus, proper folding of the alpha-helical domain of apoB-100 is essential for efficient secretion.

Modulation of aortic vascular reactivity by sex hormones in a male rat model of metabolic syndrome

Modulation by sex hormones of aortic reactivity in rats with the metabolic syndrome (MS) was investigated. The following groups of weanling male Wistar rats were used: control rats (C) received regular tap water while MS rats received 30% sucrose in their drinking water; both had rodent chow for 24 weeks. These two groups were further subdivided into the following four groups: intact (Int), castrated (Cas), castrated plus testosterone (T) and castrated plus estradiol (E). Vascular response of thoracic aortic rings to norepinephrine (NE), acetylcholine (ACh), indomethacin (Indo) and nitro-l-arginine-methyl ester (L-NAME) was investigated. Blood pressure (BP) and serum nitrates and nitrites were measured. BP and serum nitrates and nitrites were modified by castration and treatments with either T or E. Vasoconstriction in Int MS and Cas MS+T aortas was larger than in C and Cas C+T, respectively. Vasodilation in Int MS and Cas MS+T was reduced in comparison with C and Cas C+T, Cas MS and Cas MS+E. Indomethacin decreased vasoconstriction in all groups (P<0.002) but Int C and Cas C+T remained significantly smaller than Int MS and Cas MS+T. l-NAME in NE-contracted vessels induced a significant increase in vasoconstriction, except in Cas C+E rats; the responses of Int MS and Cas MS+T were significantly larger than in Int C and Cas C+T. The results suggest endothelial dysfunction in Int MS and Cas MS+T and a protective effect resulting from castration and castration plus E in MS animals, indicating a sex hormone influence.

Hypertriglyceridemia: its etiology, effects and treatment

Elevated plasma triglyceride concentration is a common biochemical finding, but the evidence for the benefit of treating this lipid disturbance remains less robust than that for treating elevated low-density lipoprotein-cholesterol. Part of the difficulty in the provision of specific recommendations has been the frequent coexistence of elevated triglycerides with other conditions that affect cardiovascular disease risk, such as depressed high-density lipoprotein-cholesterol, obesity, metabolic syndrome, proinflammatory and prothrombotic biomarkers, and type 2 diabetes. Recent investigations of outcomes of cardiovascular disease when medications are used to reduce triglyceride levels suggest that, although a net benefit probably exists, both relative and absolute risk reductions seem underwhelming when compared with the benefit of reducing low-density lipoprotein-cholesterol levels with treatment. However, the totality of evidence suggests that elevated triglyceride levels likely contribute independently to increased risk of cardiovascular disease, although there is no consensus about appropriate target levels. Furthermore, severe hypertriglyceridemia is associated with an increased risk of acute pancreatitis, irrespective of its effect on risk of cardiovascular disease. We review the causes and classification of elevated triglyceride levels, the clinical manifestations of primary hypertriglyceridemia and the management of patients with elevated triglyceride levels.

Consistent Effects of Genes Involved in Reverse Cholesterol Transport on Plasma Lipid and Apolipoprotein Levels in CARDIA Participants

OBJECTIVE

To identify common variations in genes in the reverse cholesterol transport pathway with nongender-specific influence on plasma lipid and apolipoprotein levels.

METHODS AND RESULTS

An average of 5 single nucleotide polymorphisms (SNPs) were genotyped within each of 45 genomic regions (54 genes) in blacks (1131 females and 812 males) and whites (1102 females and 954 males) from the Coronary Artery Risk Development in Young Adults (CARDIA) study. SNPs and gene-based 3-SNP haplotypes were evaluated for their ability to predict variation in plasma apolipoproteins (apo) A-I and apoB, total cholesterol (TC), high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides (TG). We identified 14 SNPs in 6 candidate gene regions that explained statistically significant variation in the same trait in both genders of at least one race and with evidence of consistent genotype mean trend across gender within race. Haplotype analyses identified 9 candidate gene regions that explained statistically significant variation in one or both races.

CONCLUSIONS

Four gene regions, ABCA1, APOA1/C3/A4/A5, APOE/C1/C4/C2, and CETP, explained plasma lipoprotein variation most consistently across strata. Other gene regions that influence plasma lipid and apolipoprotein levels within race include CYP7A1, LPL, PPARA, SOAT1, and SREBF2.

Association of nucleotide variations in the apolipoprotein B48 receptor gene (APOB48R) with hypercholesterolemia

Factors predisposing to the phenotypic features of high total cholesterol (T-Cho) in human plasma have not been clearly defined. Here we report an association between two variations in the apolipoprotein B48 receptor gene (APOB48R) and plasma T-Cho levels among 352 adult individuals in Japan. By analyzing phenotypic associations between age- and gender-adjusted levels of plasma T-Cho, low-density lipoprotein (LDL) cholesterol (LDL-C), and high-density lipoprotein (HDL) cholesterol (HDL-C), we detected a significant correlation between genotypes of the A419P variation and adjusted T-Cho levels. Among homozygous G-allele carriers (n=265), heterozygous carriers (n=78), and homozygous minor C-allele carriers (n=9), T-Cho levels were 2.43+/-0.21 mg/cm(3), 2.48+/-0.24 mg/cm(3), and 2.63+/-0.21 mg/cm(3), respectively, indicating a codominant T-Cho-elevating effect of the minor C-allele (r=0.15, P=0.007). A similar effect was detected for c.934-960/del (r=0.13, P=0.015). Linkage disequilibrium (LD) analysis detected significant LD among eight variant sites that included neighboring loci. Our results indicate that variations in APOB48R and nearby genes are among the many factors involved in hypercholesterolemia. The etiological studies should now include consideration of this novel aspect of the mechanism(s) leading to hypercholesterolemic disease.

Alcohol intake modulates the genetic association between HDL cholesterol and the PPARgamma2 Pro12Ala polymorphism

The peroxisome proliferator-activated receptor gamma (PPARgamma) Pro12Ala polymorphism affects plasma lipids, but to what extent alcohol intake interferes with this association remains unknown. We randomly recruited 251 nuclear families (433 parents and 493 offspring) in the framework of the European Project on Genes in Hypertension study and genotyped 926 participants in whom all serum lipid variables and information on alcohol consumption were available for PPARgamma2 Pro12Ala. Genotype-phenotype relations were assessed using generalized estimating equations (GEE) and a quantitative transmission disequilibrium test (QTDT). The Ala12 allele was more frequent in Novosibirsk (0.17) than in Cracow (0.12) and Mirano (0.11) (P < 0.01). Using GEE (P = 0.03) or QTDT (P = 0.007), Italian offspring carrying the Ala12 allele had higher serum HDL cholesterol than noncarriers. HDL cholesterol levels were on average 0.086 mmol/l (P = 0.001) higher in drinkers than in nondrinkers. Compared with Pro12 homozygotes, Ala12 allele carriers consuming alcohol had higher serum total and HDL cholesterol, with the opposite trend occurring in nondrinkers. This genotype-alcohol interaction was independent of the type of alcoholic beverage and more pronounced in moderate than in heavy drinkers. We conclude that alcohol intake modulates the relation between the PPARgamma2 Pro12Ala and HDL cholesterol level and that, therefore, the Pro12Ala polymorphism, pending confirmation of our findings, might affect cardiovascular prognosis.

Locus for quantitative HDL-cholesterol on chromosome 10q in Finnish families with dyslipidemia

Decreased HDL-cholesterol (HDL-C) and familial combined hyperlipidemia (FCHL) are the two most common familial dyslipidemias predisposing to premature coronary heart disease (CHD). These dyslipidemias share many phenotypic features, suggesting a partially overlapping molecular pathogenesis. This was supported by our previous pooled data analysis of the genome scans for low HDL-C and FCHL, which identified three shared chromosomal regions for a qualitative HDL-C trait on 8q23.1, 16q23.3, and 20q13.32. This study further investigates these regions as well as two other loci we identified earlier for premature CHD on 2q31 and Xq24 and a locus for high serum triglycerides (TGs) on 10q11. We analyzed 67 microsatellite markers in an extended study sample of 1,109 individuals from 92 low HDL-C or FCHL families using both qualitative and quantitative lipid phenotypes. These analyses provided evidence for linkage (a logarithm of odds score of 3.2) on 10q11 using a quantitative HDL-C trait. Importantly, this region, previously linked to TGs, body mass index, and obesity, provided evidence for association for quantitative TGs (P = 0.0006) and for a combined trait of HDL-C and TGs (P = 0.008) with marker D10S546. Suggestive evidence for linkage also emerged for HDL-C on 2q31 and for TGs on 20q13.32. Finnish families ascertained for dyslipidemias thus suggest that 10q11, 2q31, and 20q13.32 harbor loci for HDL-C and TGs.

A genome-wide scan of serum lipid levels in the Old Order Amish

Elevated serum low density lipoprotein cholesterol (LDL-C) and triglyceride (TG) and decreased high density lipoprotein cholesterol (HDL-C) levels are established risk factors for cardiovascular disease (CVD). To identify quantitative trait loci influencing lipid levels, we conducted genome-wide linkage analyses of total serum cholesterol (TSC), HDL-C, ln-transformed TG (LNTG) and LDL-C levels in 612 individuals from 28 families of the Amish Family Diabetes Study (AFDS). Subjects were genotyped for 373 microsatellite markers covering all 22 autosomes and the X chromosome at an average density of 9.7 centimorgans. All lipid traits exhibited moderate estimated heritability (h2 +/- S.E.): TSC, 0.63 +/- 0.11; HDL-C, 0.54 +/- 0.08; LNTG, 0.37 +/- 0.08; LDL-C, 0.62 +/- 0.10. The highest logarithm of the odds (LOD) score observed was 2.47 (P = 0.0003), at 3p25 for LDL-C. LOD scores exceeding 2.0 (P < 0.001) were also observed at 2p23 (LOD = 2.17) and 19p13 (LOD = 2.23) for LDL-C, and at 11q23 (LOD = 2.03) for LNTG. Three additional regions exhibited LOD scores greater than 1.5, corresponding to a P-value of <0.005. Many of the regions suggestively linked in this genome-wide scan contain genes encoding proteins with established roles in lipid metabolism, including apolipoproteins, peroxisome proliferater-activated receptor-gamma and the LDL receptor.

Molecular Genetics of Late-Onset Alzheimer's Disease

Late-onset Alzheimer's disease (AD) is a complex and multifactorial disease with the possible involvement of several genes. Apolipoprotein E (APOE), especially the APOE*4 allele, has been established as a strong susceptibility marker that accounts for nearly 30% of the risk in late-onset AD. However, as the APOE*4 allele is neither necessary nor sufficient for the development of AD, it emphasizes the involvement of other genetic and/or environmental factors which, alone or in conjunction with APOE*4, can modify the risk of AD. Recently, genome-wide linkage or linkage disequilibrium studies on late-onset AD have provided informative data for the existence of multiple putative genes for AD on several chromosomes, with the strongest evidence on chromosomes 12, 10, 9 and 6. This paper attempts to review the current progress on the identification of additional genetic loci for late-onset AD.

Hypertriglyceridemia associated with amino acid variation Asn985Tyr of the RP1 gene

Factors predisposing to the phenotypic features of hypertriglyceridemia have not been clearly defined. Here we report an association between a missense coding region polymorphism Asn985Tyr in the retinitis pigmentosa 1 gene ( RP1) and plasma triglyceride (TG) levels in 332 adult individuals from an east-central area of Japan. Age and gender-adjusted levels of LDL-cholesterol, TG, and HDL-cholesterol were analyzed. When we separate the subjects into two genotypic groups regarding this amino acid variation, those who lack the 985-Asn allele (asparagine at residue 985) had significantly higher plasma TG levels than the others who had at least one 985-Asn allele (mean: 175.8 mg/dl vs 123.3 mg/dl; P=0.0006, Mann-Whitney test). Similarly, the former subjects had significantly lower HDL-cholesterol levels than the latter (mean: 48.0 mg/dl vs 53.8 mg/dl; P=0.038). Of the 280 individuals without a 985-Asn allele, approximately half of the individuals presented with hypertriglyceridemia, whereas only a quarter were hypertriglyceridemic among 52 individuals with the 985-Asn allele ( P=0.04). Although this SNP marker may itself be in linkage disequilibrium with other unexamined functional variants within this locus, our data suggest that genetic variation at the RP1 locus is one of the likely candidate determinants for plasma triglyceride and HDL-cholesterol metabolisms.

Evidence for bivariate linkage of obesity and HDL-C levels in the Framingham Heart Study

Background

Epidemiological studies have indicated that obesity and low high-density lipoprotein (HDL) levels are strong cardiovascular risk factors, and that these traits are inversely correlated. Despite the belief that these traits are correlated in part due to pleiotropy, knowledge on specific genes commonly affecting obesity and dyslipidemia is very limited. To address this issue, we first conducted univariate multipoint linkage analysis for body mass index (BMI) and HDL-C to identify loci influencing variation in these phenotypes using Framingham Heart Study data relating to 1702 subjects distributed across 330 pedigrees. Subsequently, we performed bivariate multipoint linkage analysis to detect common loci influencing covariation between these two traits.

Results

We scanned the genome and identified a major locus near marker D6S1009 influencing variation in BMI (LOD = 3.9) using the program SOLAR. We also identified a major locus for HDL-C near marker D2S1334 on chromosome 2 (LOD = 3.5) and another region near marker D6S1009 on chromosome 6 with suggestive evidence for linkage (LOD = 2.7). Since these two phenotypes have been independently mapped to the same region on chromosome 6q, we used the bivariate multipoint linkage approach using SOLAR. The bivariate linkage analysis of BMI and HDL-C implicated the genetic region near marker D6S1009 as harboring a major gene commonly influencing these phenotypes (bivariate LOD = 6.2; LOD_eq = 5.5) and appears to improve power to map the correlated traits to a region, precisely.

Conclusions

We found substantial evidence for a quantitative trait locus with pleiotropic effects, which appears to influence both BMI and HDL-C phenotypes in the Framingham data.