[Regulation of apolipoprotein expression].
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Pathogenesis
Apolipoprotein E
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Apolipoprotein C2
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Plasma lipoprotein
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Purpose: To review DNA analysis of apolipoprotein E used to assess patients with hyperlipidemia. Data Sources and Study Selection: 44 basic science studies of molecular analysis; 42 basic science studies of the biochemical, cellular biological, and molecular biological features of apolipoprotein E; and 29 clinical investigational studies, meta-analyses, and case series of patients with mutations in apolipoprotein E. Data Extraction: Methods of DNA analysis were reviewed, using specific examples in human disease, and the role of apolipoprotein E in normal and disordered lipoprotein metabolism was reviewed. Genetic analysis of apolipoprotein E in populations and particularly in persons with type III hyperlipoproteinemia is reviewed. Data Synthesis: In the general population, common DNA variants of apolipoprotein E are consistently associated with modest differences in plasma lipids and lipoproteins. Homozygosity for the E2 isoform of apolipoprotein E predisposes some patients to the development of type III hyperlipoproteinemia, a condition that involves an additional genetic or environmental factor for full clinical expression. Rare mutations of apolipoprotein E also cause hyperlipidemia. Conclusions: DNA variation of apolipoprotein E is one of several genetic and environmental factors that interact in a complex manner to affect plasma lipoproteins. DNA analysis of apolipoprotein E can be used in persons with hyperlipidemia to identify those with type III hyperlipoproteinemia and in relatives of affected persons to identify those who are predisposed.
Hyperlipidemia
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We have used a common TaqI restriction fragment length polymorphism (RFLP) near the human apolipoprotein C-II (apoC-II) gene to study linkage with apolipoprotein E (apoE). The inheritance of the apoC-II RFLP was followed in seven families that were segregating for apoE protein variants. No recombinants were observed in 20 informative meioses, giving an overall lod score of greater than 4.0 at recombination fraction 0. We have also observed apparent linkage disequilibrium between apoE and the apoC-II RFLP. Taken together these results demonstrate that these two apolipoprotein genes are closely linked and confirm that the gene for apoC-II is on human chromosome 19.
TaqI
Linkage Disequilibrium
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Genetic linkage
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Recombination Fraction
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Atherosclerotic cardiovascular disease
ATHEROSCLEROTIC VASCULAR DISEASE
Vascular Medicine
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Apolipoprotein E
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Low density and very low density lipoproteins contain apolipoprotein B 100 which is synthesized in the liver. Chylomicrons have apolipoprotein B 48 , which consists of part of the apolipoprotein B 100 sequence, and which is produced in the gut by the same gene that encodes for apolipoprotein B 100 . Both apolipoprotein B 100 and apolipoprotein B 48 are important for the secretion of triglyceride-rich lipoproteins whereas apolipoprotein B 100 , which can bind to the low density lipoprotein receptor, is also important for low density lipoprotein catabolism. Apolipoprotein (a) has structural homology with plasminogen and exists as a complex with apolipoprotein B 100 in lipoprotein (a). Apolipoprotein AI is the main lipoprotein in high density lipoproteins, whilst apolipoprotein E, present in chylomicrons and intermediate density lipoproteins, plays a major role in their catabolism. Serum apolipoprotein B and apolipoprotein AI have potential in the evaluation of coronary risk. Apolipoprotein B may be of particular value in patients with hypertriglyceridaemia and normal low density lipoprotein cholesterol levels. Apolipoprotein (a) has also been reported to be an important indicator of coronary risk, especially in the presence of elevated apolipoprotein B. Lack of standardization and the limited availability of prospective data at present limit the routine use of apolipoprotein B, AI and (a) measurements. The determination of apolipoprotein E phenotypes has proved useful in the diagnosis of remnant (type III) hyperlipoproteinaemia.
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Apolipoprotein C2
Coding region
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To describe the roles of apolipoprotein C-III (apoC-III) and apoE in VLDL and LDL metabolismApoC-III can block clearance from the circulation of apolipoprotein B (apoB) lipoproteins, whereas apoE mediates their clearance. Normolipidemia is sustained by hepatic secretion of VLDL and IDL subspecies that contain both apoE and apoC-III (VLDL E+C-III+). Most of this VLDL E+C-III+ is speedily lipolyzed, reduced in apoC-III content, and cleared from the circulation as apoE containing dense VLDL, IDL, and light LDL. In contrast, in hypertriglyceridemia, most VLDL is secreted with apoC-III but without apoE, and so it is not cleared until it loses apoC-III during lipolysis to dense LDL. In normolipidemia, the liver also secretes IDL and large and medium-size LDL, whereas in hypertriglyceridemia, the liver secretes more dense LDL with and without apoC-III. These pathways establish the hypertriglyceridemic phenotype and link it metabolically to dense LDL. Dietary carbohydrate compared with unsaturated fat suppresses metabolic pathways mediated by apoE that are qualitatively similar to those suppressed in hypertriglyceridemia.The opposing actions of apoC-III and apoE on subspecies of VLDL and LDL, and the direct secretion of LDL in several sizes, establish much of the basic structure of human apoB lipoprotein metabolism in normal and hypertriglyceridemic humans.
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Apolipoprotein E
Catabolism
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Apolipoprotein (apo)E polymorphism has been shown to be associated with different serum levels of cholesterol, apoB, and apoE. In clarifying the degree of influence of the apoE isoforms, investigations in an early stage of life are useful. The aim of the study was to investigate the plasma levels of apoB and apoA-I as structural proteins of low and high density lipoproteins, in relation to apoE phenotypes during the first year of life. Conclusions about the relationship between apoE phenotype and the development of the lipoprotein patterns can be drawn. The concentrations of apoB and apoA-I in capillary plasma as well as the apoE phenotype were estimated in 199 newborns (7 days old) and in follow-up investigations of a subgroup of 45 at 1, 4, 12, 24, and 52 weeks. The phenotype frequencies were as follows: 70% apoE 3/3, 16% apoE 3/4, 10% apoE 2/3, 2.5% apoE 2/2, and 1.5% apoE 4/2. The plasma concentrations of apoB and apoA-I in the newborns (7 days old) averaged 55% of the adult value and increased toward the end of the first year of life up to approximately 85%. The course of the plasma concentrations of apoB and apoA-I in relation to the apoE phenotype showed that, beginning at 24 weeks, the apoB levels were significantly lower for the phenotype E 2/2 and in tendency also for the phenotype E 2/3 in comparison with E 3/3. At the end of the first year of life, the apoB levels in infants with apoE phenotype 2/2 increased only by 50% and yielded 0.59 g/L.(ABSTRACT TRUNCATED AT 250 WORDS)
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