Free Cholesterol In Large Vldl
Background
Section titled “Background”Cholesterol is a vital lipid, serving as a structural component of cell membranes and a precursor for hormones and vitamin D. It is transported throughout the body by lipoproteins, which are spherical particles composed of lipids and proteins. Very Low-Density Lipoproteins (VLDL) are one such type of lipoprotein, primarily responsible for transporting triglycerides and cholesterol (including free cholesterol) synthesized in the liver to various tissues in the body. “Large VLDL” refers to the largest, most triglyceride-rich VLDL particles, which play a significant role in the initial stages of lipid transport and metabolism. Understanding the dynamics of free cholesterol within these large VLDL particles is crucial for assessing overall lipid health and cardiovascular risk.
Biological Basis
Section titled “Biological Basis”Large VLDL particles are assembled and secreted by the liver. They contain a core of triglycerides and cholesterol esters, surrounded by a monolayer of phospholipids, free cholesterol, and apolipoproteins. Once in circulation, VLDL particles interact with enzymes like lipoprotein lipase, which removes triglycerides, causing the VLDL to shrink and become relatively enriched in cholesterol. This process eventually transforms VLDL into intermediate-density lipoproteins (IDL) and then low-density lipoproteins (LDL), both of which continue to carry cholesterol. Genetic variations can influence the production, composition, and clearance of VLDL, thereby affecting the levels of free cholesterol within these particles and subsequently impacting overall lipid profiles.
Genome-wide association studies have identified numerous genetic loci associated with lipid concentrations, including LDL cholesterol and triglycerides, which are closely linked to VLDL metabolism. [1]For example, common single nucleotide polymorphisms (SNPs) in a region on chromosome 1p13, encompassing genes such asCELSR2, PSRC1, MYBPHL, and SORT1, have been robustly associated with LDL cholesterol levels. [1] Other genes like APOB, LDLR, HMGCR, and PCSK9 also have established roles in LDL cholesterol regulation. [1] Variations in genes such as MLXIPL, LPL, GCKR, TRIB1, GALNT2, CILP2, PBX4, and ANGPTL3have been linked to triglyceride concentrations.[2] These genetic factors collectively influence the complex pathways of VLDL synthesis, remodeling, and cholesterol content.
Clinical Relevance
Section titled “Clinical Relevance”Elevated levels of VLDL, particularly large, triglyceride-rich VLDL particles and their associated cholesterol content, are a key feature of dyslipidemia. Dyslipidemia, an imbalance of lipids in the blood, is a major risk factor for cardiovascular disease (CVD), including coronary artery disease.[3]Genetic predispositions that lead to higher VLDL cholesterol can contribute to the development and progression of atherosclerosis, the hardening and narrowing of arteries. Identifying and understanding these genetic influences can help in assessing an individual’s risk for CVD and guiding preventive or therapeutic interventions. For instance, specific alleles associated with increased LDL cholesterol, which is derived from VLDL, have also been linked to an increased risk of coronary artery disease.[1]
Social Importance
Section titled “Social Importance”Cardiovascular diseases remain a leading cause of morbidity and mortality worldwide, posing a significant public health challenge. Understanding the genetic and metabolic factors that influence lipid levels, such as free cholesterol in large VLDL, is crucial for developing more effective strategies for prevention, diagnosis, and treatment. Genetic insights can contribute to personalized medicine approaches, allowing for earlier identification of individuals at higher risk and tailoring interventions based on their specific genetic profile. This knowledge can empower individuals and healthcare providers to make informed decisions regarding diet, lifestyle, and medication to mitigate the impact of dyslipidemia and associated cardiovascular risks.
Limitations
Section titled “Limitations”Methodological and Statistical Considerations
Section titled “Methodological and Statistical Considerations”The identification of genetic variants influencing free cholesterol in large VLDL is constrained by the statistical power inherent in the study designs. While meta-analyses combined data from multiple cohorts, achieving substantial sample sizes for gene discovery and replication (e.g., up to 19,840 for initial discovery and 20,623 for replication), the research acknowledges that “sequence variants could be identified with larger samples and improved statistical power for gene discovery”.[4]This suggests that the current sample sizes may still be insufficient to detect all variants with smaller effect sizes or to fully elucidate the polygenic architecture of this specific lipid trait. Furthermore, technical challenges during the replication phase, such as the inability to design primers or probes for certain promising single nucleotide polymorphisms (SNPs) like those nearGRIN3A, LCAT, and FARS2, meant that some potentially significant associations could not be confirmed, leading to potential gaps in the understanding of the genetic landscape. [5]
Variations in analytical approaches across different cohorts also introduce a degree of heterogeneity in the meta-analyses. For instance, some replication cohorts did not consistently account for all covariates, such as the square of age (age2), and applied different criteria for outlier exclusion. [5] Additionally, the availability and consideration of information on lipid-lowering therapy varied, with some studies lacking this crucial data. [5]Although genomic control parameters were generally low, indicating minimal residual confounding from population stratification, these inconsistencies in statistical modeling and data handling across contributing studies could subtly impact the combined effect estimates and reduce the precision of the overall findings for free cholesterol in large VLDL.
Phenotypic Definition and Measurement Challenges
Section titled “Phenotypic Definition and Measurement Challenges”The assessment of free cholesterol in large VLDL faces limitations related to phenotype definition and measurement protocols. A significant challenge arises from the treatment of individuals on lipid-lowering therapy; most studies either excluded these participants or imputed their untreated lipid values, as seen in the FHS cohort.[4] While this approach aims to isolate genetic effects, it restricts the generalizability of findings to the subset of the population not receiving such medications, which may not accurately reflect real-world clinical scenarios where these therapies are prevalent. The lack of consistent information on lipid-lowering therapy across all cohorts further complicates the interpretation of combined results. [5]
Moreover, the analytical process for lipid phenotypes often involves transformations and adjustments that can impact direct physiological interpretation. Triglyceride levels, for example, were frequently log-transformed, and the primary phenotypes used for genotype-phenotype association analyses were standardized residuals adjusted for covariates like age, sex, and ancestry components.[4]While these adjustments are crucial for controlling confounding factors and reducing error variance, analyzing residual values rather than raw concentrations means the direct biological effects on circulating free cholesterol in large VLDL are inferred indirectly. Furthermore, the requirement for fasting blood samples, while standard, highlights a practical constraint; inconsistent fasting status across participants could introduce variability if not rigorously controlled, potentially influencing the accuracy of lipid measurements.[6]
Generalizability and Unexplained Variation
Section titled “Generalizability and Unexplained Variation”A primary limitation of the current research on lipid traits, including free cholesterol in large VLDL, is its restricted generalizability due to a predominant focus on individuals of European ancestry.[4] Studies explicitly excluded individuals of non-European ancestry [4] and investigations into different ancestral groups have shown distinct linkage disequilibrium patterns, indicating that genetic associations identified in European populations may not be directly transferable or hold the same predictive power in other ethnicities. [7]This narrow demographic scope limits the applicability of the findings to a global population and underscores the need for diverse cohorts to fully understand the genetic contributions to free cholesterol in large VLDL across varied ancestral backgrounds.
Despite the identification of numerous genetic loci, the collective contribution of these variants explains only a modest proportion of the overall variability in lipid phenotypes. For example, the identified loci account for approximately 7.7% of the variance in LDL cholesterol, 9.3% for HDL cholesterol, and 7.4% for triglycerides [4] with another study reporting 6% of total variability. [8]This substantial “missing heritability” suggests that a large fraction of the genetic and environmental factors influencing free cholesterol in large VLDL remains uncharacterized. Unmeasured environmental influences, complex gene-environment interactions, epigenetic modifications, or rare genetic variants that were not detectable with current methods likely contribute significantly to the unexplained variance, representing a substantial knowledge gap in the comprehensive understanding of this trait. Furthermore, the broader health implications of these lipid variants, such as their associations with longevity or stroke, require further dedicated investigation.[1]
Variants
Section titled “Variants”Genetic variations play a crucial role in determining an individual’s lipid profile, including the levels of free cholesterol within large VLDL particles. These variants often influence genes involved in lipoprotein synthesis, metabolism, and clearance, as well as broader metabolic pathways. Understanding these genetic associations helps illuminate the complex mechanisms underlying dyslipidemia and cardiovascular risk.
Several variants are found in genes central to lipoprotein structure and metabolism. TheAPOBgene encodes apolipoprotein B, a foundational protein for VLDL, IDL, and LDL particles, essential for their assembly and receptor binding. Thers676210 variant in APOBcan influence the production and clearance of these lipoproteins, thereby directly impacting the amount of free cholesterol in large VLDL by affecting particle formation and secretion.[8] Similarly, the LPLgene, which codes for lipoprotein lipase, is vital for breaking down triglycerides in VLDL. Itsrs117026536 variant can alter enzyme activity, thereby affecting VLDL remodeling and the release of free cholesterol during the process of lipolysis.[8] The APOE-APOC1 gene cluster, including the rs1065853 variant, is crucial for the metabolism of triglyceride-rich lipoproteins;APOE facilitates the removal of VLDL remnants, while APOC1modulates this process, with variations impacting the overall clearance and composition of VLDL and its free cholesterol content. Furthermore,LPA variants such as rs10455872 and rs73596816 are associated with circulating levels of lipoprotein(a), a modified LDL particle that can interfere with cholesterol transport and indirectly influence the overall lipid environment, including free cholesterol within large VLDL particles. TheLPAL2 gene, with its variant rs117733303 , is also implicated in lipoprotein metabolism, potentially through mechanisms that affect the assembly or remodeling of lipid particles, thereby contributing to variations in free cholesterol.
Other genes regulate key metabolic pathways that significantly influence lipid synthesis and glucose homeostasis. TheGCKRgene encodes glucokinase regulatory protein, which controls the activity of glucokinase, a critical enzyme for glucose phosphorylation in the liver.[8] The rs1260326 variant in GCKRis associated with altered triglyceride levels and liver fat, which can lead to increased hepatic VLDL production and, consequently, higher free cholesterol in large VLDL particles. TheMLXIPLgene, also known as ChREBP, is a transcription factor that activates genes involved in fatty acid and triglyceride synthesis in response to glucose. Itsrs34060476 variant is a significant factor in regulating VLDL production and composition, directly affecting the amount of free cholesterol carried.[8] Similarly, variants within the TRIB1AL gene, such as rs28601761 , are strongly linked to plasma lipid levels, including triglycerides and cholesterol. TRIB1plays a role in the degradation of transcription factors that regulate lipid synthesis, and its modulation can affect hepatic VLDL secretion and the amount of free cholesterol carried by these large particles.
Finally, genes like ZPR1 and DOCK7 have emerging roles that can indirectly affect lipid profiles, contributing to the complexity of metabolic regulation. The ZPR1 gene (rs964184 ) is involved in fundamental cellular processes like proliferation and survival, and disruptions in these processes can have downstream effects on metabolic health, including the regulation of lipid synthesis and transport, thereby influencing free cholesterol in large VLDL.[8] The DOCK7 gene (rs11207997 ) is primarily known for its role in neuronal development; however, recent research suggests broader metabolic implications, potentially influencing adipogenesis or insulin sensitivity. Such effects can indirectly alter the liver’s production of VLDL and its cholesterol content, linking these variants to overall lipid homeostasis and the characteristics of circulating lipoproteins.[8] These diverse genetic associations underscore the intricate interplay of multiple pathways in shaping an individual’s lipid profile and the specific characteristics of circulating lipoproteins.
Key Variants
Section titled “Key Variants”| RS ID | Gene | Related Traits |
|---|---|---|
| rs964184 | ZPR1 | very long-chain saturated fatty acid measurement coronary artery calcification vitamin K measurement total cholesterol measurement triglyceride measurement |
| rs1260326 | GCKR | urate measurement total blood protein measurement serum albumin amount coronary artery calcification lipid measurement |
| rs115849089 | LPL - RPL30P9 | high density lipoprotein cholesterol measurement triglyceride measurement mean corpuscular hemoglobin concentration Red cell distribution width lipid measurement |
| rs328 rs144503444 | LPL | high density lipoprotein cholesterol measurement triglyceride measurement level of phosphatidylcholine sphingomyelin measurement diacylglycerol 36:2 measurement |
| rs2954021 rs28601761 | TRIB1AL | low density lipoprotein cholesterol measurement serum alanine aminotransferase amount alkaline phosphatase measurement body mass index Red cell distribution width |
| rs676210 | APOB | lipid measurement low density lipoprotein cholesterol measurement level of phosphatidylethanolamine depressive symptom measurement, non-high density lipoprotein cholesterol measurement anxiety measurement, triglyceride measurement |
| rs10455872 | LPA | myocardial infarction lipoprotein-associated phospholipase A(2) measurement response to statin lipoprotein A measurement parental longevity |
| rs584007 | APOE - APOC1 | alkaline phosphatase measurement sphingomyelin measurement triglyceride measurement apolipoprotein A 1 measurement apolipoprotein B measurement |
| rs13240065 rs34060476 | MLXIPL | amount of growth arrest-specific protein 6 (human) in blood level of phosphatidylcholine-sterol acyltransferase in blood hepatocyte growth factor-like protein amount alcohol consumption quality triacylglycerol 52:4 measurement |
| rs821840 rs183130 | HERPUD1 - CETP | triglyceride measurement total cholesterol measurement high density lipoprotein cholesterol measurement low density lipoprotein cholesterol measurement metabolic syndrome |
Classification, Definition, and Terminology
Section titled “Classification, Definition, and Terminology”Lipoprotein Metabolism and Cholesterol Transport
Section titled “Lipoprotein Metabolism and Cholesterol Transport”Lipoproteins are complex particles that transport lipids, including cholesterol and triglycerides, through the bloodstream. Very low-density lipoproteins (VLDL) are primarily responsible for carrying triglycerides synthesized in the liver to peripheral tissues, but they also contain cholesterol. The metabolism of these lipoproteins is a finely tuned process critical for maintaining energy balance and cellular function throughout the body. [9]Disruptions in this transport system can lead to an accumulation of lipids in the blood, contributing to various systemic consequences, particularly cardiovascular disease. The composition of VLDL, including its free cholesterol content, reflects the dynamic interplay of synthesis, modification, and clearance pathways.
The liver plays a central role in synthesizing VLDL particles, which are then released into circulation. As VLDL circulates, enzymes act upon it, removing triglycerides and altering its composition, eventually transforming it into intermediate-density lipoprotein (IDL) and then low-density lipoprotein (LDL). This metabolic cascade ensures that lipids are delivered to cells that require them for energy, membrane synthesis, or hormone production. The balance of this system is crucial, as both the quantity and quality of circulating lipoproteins, including free cholesterol within VLDL, are vital indicators of metabolic health.[3]
Genetic Regulation of Lipid Homeostasis
Section titled “Genetic Regulation of Lipid Homeostasis”Plasma lipid levels exhibit high heritability, indicating a strong genetic influence on their concentrations in the blood. [3]Genome-wide association studies (GWAS) have identified numerous genetic loci and specific genes associated with variations in high-density lipoprotein (HDL) cholesterol, LDL cholesterol, and triglycerides. These include genes such asABCA1, APOB, CELSR2, CETP, DOCK7, GALNT2, GCKR, HMGCR, LDLR, LIPC, LIPG, LPL, MLXIPL, NCAN, PCSK9, and TRIB1, among others. Variants in these genes can influence various aspects of lipid metabolism, from synthesis to uptake, thereby impacting the levels of free cholesterol in lipoproteins like large VLDL.[3]
Specific genetic mechanisms include the impact of transcription factors and regulatory elements on gene expression. For instance, MLXIPLencodes a protein that binds to and activates specific motifs in the promoters of triglyceride synthesis genes, directly affecting the lipid cargo of newly formed VLDL particles.[1] Similarly, the transcription factor MAFB has been shown to interact with LDL-related protein, though its precise mechanism for influencing LDL cholesterol, and by extension VLDL remnants, requires further definition. [5] Variations in genes like HMGCR can also affect alternative splicing, which in turn influences LDL cholesterol levels, highlighting the intricate regulatory networks at play in lipid homeostasis. [7]
Key Proteins and Enzymatic Pathways in Lipoprotein Processing
Section titled “Key Proteins and Enzymatic Pathways in Lipoprotein Processing”The precise regulation of lipoprotein metabolism relies on a network of critical proteins, enzymes, and receptors. Apolipoprotein C-III, encoded byAPOC3, is a key modulator of triglyceride metabolism. A null mutation in humanAPOC3has been shown to result in a favorable plasma lipid profile and offer apparent cardioprotection, suggesting its significant role in VLDL catabolism and triglyceride clearance.[10] Another crucial protein is Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9), which accelerates the degradation of the LDL receptor (LDLR), thereby influencing the clearance of LDL and its precursors like VLDL remnants from the bloodstream. [11]
Enzymatic activities also play a vital role. Angiopoietin-like 4 protein (ANGPTL4) is known to inhibit lipoprotein lipase, an enzyme critical for hydrolyzing triglycerides from VLDL particles. Thus, variations affectingANGPTL4can alter the rate at which VLDL is metabolized, impacting its size and cholesterol content.[5] In the context of cholesterol synthesis, MVK (mevalonate kinase) catalyzes an early step in the pathway, while MMABparticipates in cholesterol degradation, demonstrating how metabolic processes directly control the availability of cholesterol for lipoprotein assembly.[1] Lecithin-cholesterol acyltransferase (LCAT) is another enzyme with a well-established role in lipid metabolism, influencing the esterification of cholesterol within lipoproteins and affecting overall lipid concentrations. [1]
Pathophysiological Implications of Dyslipidemia
Section titled “Pathophysiological Implications of Dyslipidemia”Dyslipidemia, characterized by abnormal levels of circulating lipids, including altered free cholesterol in large VLDL, is a major risk factor for cardiovascular disease (CVD).[1]Atherosclerosis, the underlying pathology for conditions like coronary artery disease and stroke, involves the cumulative deposition of LDL cholesterol in arterial walls.[1]While LDL is directly implicated, the preceding VLDL and its remnants contribute to the atherogenic process, particularly when their metabolism is disrupted, leading to prolonged circulation and increased opportunity for arterial wall penetration. Therefore, maintaining healthy levels of all lipid components, including free cholesterol in large VLDL, is crucial for cardiovascular health.
Homeostatic disruptions in lipid metabolism can arise from both genetic predispositions and environmental factors. For instance, common variants at genes like TIMD4 and HAVCR1, which function as phosphatidylserine receptors on macrophages involved in engulfing apoptotic cells, have been associated with LDL cholesterol levels, suggesting a potential role in the inflammatory and clearance processes linked to atherosclerosis.[5]The systemic consequences of dyslipidemia extend beyond the cardiovascular system, impacting overall metabolic health and highlighting the importance of understanding the intricate mechanisms governing lipoprotein composition and function.
Pathways and Mechanisms
Section titled “Pathways and Mechanisms”Hepatic Cholesterol and Triglyceride Synthesis Pathways
Section titled “Hepatic Cholesterol and Triglyceride Synthesis Pathways”The synthesis of free cholesterol incorporated into large VLDL particles is intricately linked to hepatic metabolic pathways, primarily the mevalonate pathway. The rate-limiting enzyme in this pathway, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), dictates the flux of cholesterol biosynthesis. [12] Its activity is tightly regulated by sterol regulatory element-binding protein 2 (SREBP2), a transcription factor that also controls the expression of other key enzymes like mevalonate kinase (MVK), which catalyzes an early step in cholesterol biosynthesis, and MMAB, involved in cholesterol degradation. [1] Concurrently, the MLXIPLgene, encoding a protein that activates specific motifs in the promoters of triglyceride synthesis genes, plays a crucial role in the hepatic production of triglycerides, which are the primary cargo of large VLDL particles.[1] This coordinated biosynthesis ensures the availability of both cholesterol and triglycerides for packaging into nascent VLDL.
Lipoprotein Assembly, Remodeling, and Receptor Interactions
Section titled “Lipoprotein Assembly, Remodeling, and Receptor Interactions”Once synthesized, free cholesterol and triglycerides are assembled into nascent VLDL particles within the liver, then secreted into circulation. The remodeling of these VLDL particles, and their subsequent catabolism, significantly influences the circulating levels of free cholesterol. Apolipoprotein C-III (APOC3) is a key regulator, as a null mutation in this gene confers a favorable plasma lipid profile and apparent cardioprotection, likely by modulating triglyceride hydrolysis.[10]This process is mediated by lipoprotein lipase (LPL), an enzyme whose activity can be inhibited by proteins such as ANGPTL4, further influencing VLDL triglyceride and cholesterol content.[5] Hepatic lipase (LIPC) also plays a role in breaking down triglycerides in lipoproteins, with common genetic variants in LIPCbeing associated with concentrations of various glycerophosphatidylcholines and glycerophosphatidylethanolamines, alongside HDL cholesterol and triglyceride levels.[13]
Transcriptional Networks and Post-Translational Control
Section titled “Transcriptional Networks and Post-Translational Control”Lipid homeostasis, including the regulation of free cholesterol in VLDL, is profoundly influenced by a complex network of transcriptional and post-translational regulatory mechanisms. Transcription factors such as hepatocyte nuclear factor 4 alpha (HNF4A) and hepatocyte nuclear factor 1 alpha (HNF1A) are essential for maintaining hepatic gene expression and lipid homeostasis, with their dysregulation leading to altered plasma cholesterol levels. [5] Post-translational modifications also play a critical role, as exemplified by proprotein convertase subtilisin/kexin type 9 (PCSK9), which promotes the degradation of the low-density lipoprotein receptor (LDLR), thereby impacting the clearance of VLDL remnants and LDL. [5] Furthermore, alternative splicing, such as that affecting exon 13 of HMGCR, can influence enzyme function and cholesterol synthesis. [7]
Genetic Variation, Pathway Crosstalk, and Clinical Relevance
Section titled “Genetic Variation, Pathway Crosstalk, and Clinical Relevance”The intricate interplay between various lipid metabolic pathways and their regulatory mechanisms highlights a systems-level integration that can be perturbed by genetic variations, leading to dyslipidemia. Gene clusters, such as the APOA5-APOA4-APOC3-APOA1 region, demonstrate how multiple genes with related functions interact to modulate plasma lipid concentrations. [3]Dysregulation within these interconnected pathways, often due to common genetic variants, contributes to polygenic dyslipidemia and increases the risk of cardiovascular disease.[5] Understanding these complex interactions and identifying key regulatory nodes, such as PCSK9 or APOC3, provides critical insights for developing therapeutic targets aimed at normalizing lipid profiles and mitigating disease risk.[5]
References
Section titled “References”[1] Willer, C. J., et al. “Newly identified loci that influence lipid concentrations and risk of coronary artery disease.”Nat Genet, vol. 40, no. 2, 2008, pp. 161-69.
[2] Kooner, J. S., et al. “Genome-wide scan identifies variation in MLXIPL associated with plasma triglycerides.” Nat Genet, vol. 40, no. 2, 2008, pp. 149-51.
[3] Aulchenko, Y. S., et al. “Loci influencing lipid levels and coronary heart disease risk in 16 European population cohorts.”Nat Genet, vol. 40, no. 12, 2008, pp. 1412-20.
[4] Aulchenko, Y. S., et al. “Loci influencing lipid levels and coronary heart disease risk in 16 European population cohorts.”Nat Genet, vol. 41, no. 1, 2009, pp. 47-55.
[5] Kathiresan, S, et al. “Common variants at 30 loci contribute to polygenic dyslipidemia.” Nat Genet, vol. 40, 2008, pp. 180-188.
[6] Wallace, C., et al. “Genome-wide association study identifies genes for biomarkers of cardiovascular disease: serum urate and dyslipidemia.”Am J Hum Genet, vol. 82, no. 1, 2008, pp. 139-49.
[7] Burkhardt, R, et al. “Common SNPs in HMGCR in micronesians and whites associated with LDL-cholesterol levels affect alternative splicing of exon13.” Arterioscler Thromb Vasc Biol, vol. 28, 2008, pp. 2078-2086.
[8] Sabatti, C. et al. “Genome-wide association analysis of metabolic traits in a birth cohort from a founder population.” Nat Genet, 2009.
[9] Havel, R. J., and J. P. Kane. “Structure and Metabolism of Plasma Lipoproteins.” Harrison’s Principles of Internal Medicine, 8th ed., McGraw-Hill, 2005, chap. 114.
[10] Pollin, T. I., et al. “A null mutation in human APOC3 confers a favorable plasma lipid profile and apparent cardioprotection.” Science, vol. 322, no. 5904, 2008, pp. 1090-93.
[11] Maxwell, K. N., et al. “Overexpression of PCSK9 accelerates the degradation of the LDLR in a post-endoplasmic reticulum compartment.” Proc Natl Acad Sci USA, vol. 102, no. 6, 2005, pp. 2069-74.
[12] Goldstein, JL, and Brown MS. “Regulation of the mevalonate pathway.” Nature, vol. 343, 1990, pp. 425-430.
[13] Gieger, C, et al. “Genetics meets metabolomics: a genome-wide association study of metabolite profiles in human serum.”PLoS Genet, vol. 4, no. 11, 2008, e1000282.