Role of the apolipoprotein E polymorphism in determining normal plasma lipid and lipoprotein variation.

The structural gene locus for apolipoprotein E (apo E) is polymorphic. Three common alleles (epsilon 2, epsilon 3, epsilon 4) code for three major isoforms in plasma and determine six apo E phenotypes that may be identified by isoelectric focusing on polyacrylamide. To establish what fraction of the inherited variation in a normal plasma lipid and lipoprotein profile is attributable to the segregation of the common alleles at the apo E gene locus, we have estimated the average apo E allelic effects on plasma cholesterol (C), triglycerides, very low-density lipoprotein (VLDL)-C, VLDL-apo B, low-density lipoprotein (LDL)-C, LDL-apo B, and high-density lipoprotein (HDL)-C in a representative sample of normolipidemic individuals from Ottawa, Canada. Data from published studies were also analyzed by the same statistical procedures. As much as 16% of the genetic variance (8.3% of the total variance) for LDL-C could be accounted for by the apo E gene locus. After correction for differences in age, sex, height, and weight, it was found that the epsilon 2 allele lowered and the epsilon 4 allele raised total cholesterol, LDL-C, and LDL-apo B. No other gene has been identified that contributes as much to normal cholesterol variability. Analysis of these data and those of others also indicates that the apo E locus imparts a differential susceptibility to a variety of factors that promote hyperlipidemia. The hypothesis is proposed that the epsilon 2 allele protects against coronary heart disease (CHD) and, hence, gives a reproductive advantage that is balanced by a predisposition to CHD when the epsilon 2 is combined with a second, independent causative factor to give a reproductive disadvantage. A similar mechanism is proposed for the maintenance of the epsilon 4 allele in the population.     

Evidence for a cholesterol-lowering gene in a French-Canadian kindred with familial hypercholesterolemia

We describe a four-generation kindred with familial hypercholesterolemia (FH) in which two of the eight heterozygotes for a 5-kb deletion (exons 2 and 3) in the low density lipoprotein (LDL) receptor gene were found to have normal LDL-cholesterol levels. In our search for a gene responsible for the cholesterol-lowering effect in this family, we have studied variation in the genes encoding the LDL receptor, apolipoprotein (apo) B, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, apoAI-CIII-AIV, and lipoprotein lipase. The analysis showed that it was unlikely that variation in any of these genes was responsible for the cholesterol-lowering effect. Expression of the LDL receptor, as assessed in vitro with measurements of activity and mRNA levels, was similar in normo and hyperlipidemic subjects carrying the deletion. Analysis of the apo E isoforms revealed that most of the e2 allele carriers in this family, including the two normolipidemic 5-kb deletion carriers, were found to have LDL-cholesterol levels substantially lower than subjects with the other apo E isoforms. Thus, this kindred provides evidence for the existence of a gene or genes, including the apo e2 allele, with profound effects on LDL-cholesterol levels.C. S. and M. G. contributed equally to this work.     

Polymorphisms of apolipoproteins A-IV and E in a Turkish population living in Germany

Human apolipoproteins (apo) E and apo A-IV are polymorphic with significantly different allele frequencies among different ethnic groups. Whereas the variation at the apo E gene locus affects plasma cholesterol levels in all populations studied so far and is associated with longevity in Caucasians, the influence of the common apo A-IV polymorphism on plasma lipoproteins has not been unanimously accepted. We have therefore determined the common apo E and apo A-IV polymorphisms by isoelectric focusing, calculated the respective allele frequencies and studied their effects on plasma lipoproteins in a random sample of 240 nonrelated Turkish subjects (141 males, 99 females) living in Germany and originating from central and eastern Anatolia. When compared with the German population and other Caucasians in Europe a prominence of the apo ɛ3 allele frequency (0.885) was accompanied by a decrease in the frequencies of both the apo ɛ2 allele (0.048) and the apo ɛ4 allele (0.067). Thus, the Turkish population studied here clustered with populations mainly from southern Europe and Japan, which have low ɛ2 and ɛ4 allele frequencies. Also, the frequency of the A-IV-1 allele was higher (0.967) and that of the A-IV-2 allele lower (0.033) in the Turkish subjects studied than in other populations. At an average level of total cholesterol of 194.5 ± 45 mg/dl, no significant influence of the A-IV alleles on plasma lipoproteins was seen. However, apo E and apo B differed significantly between apo E phenotypes, with high levels of apo E and low levels of cholesterol and apo B in carriers of the ɛ2 allele, and vice versa for the ɛ4 allele. The average cholesterol excess for the ɛ2 allele was –7.95 mg/dl, for the ɛ3 allele, –1.34, and for the ɛ4 allele, +14.15 mg/dl. Thus, despite the unusual frequency distribution of the apo E alleles, their effects on plasma lipoproteins are within the range reported for other populations in Europe. Received: 10 April 1995 / Revised: 25 March 1996     

Apolipoprotein E genotypes and metabolic risk factors for coronary heart disease in middle-aged women

Apo E genotypes and plasma metabolic risk factors (total cholesterol, triglycerides, HDL and LDL cholesterol, total/HDL cholesterol ratio, lipoprotein Lp (a), apolipoprotein A-I, A-II, apo B, and apo E) were determined in 134 healthy middle-aged (X +/- SD 49.62 +/- 4.83) women. The aim of this study was to investigate metabolic risk markers according to various apo E genotypes, and to evaluate a possible risk for coronary heart disease. The results revealed that the frequencies of apo E3/3 are the most frequent (46%), followed by E4/4 (2%), E3/4 (14%), E2/3 (14%), and E2/4 (2%) in the middle-aged women. Higher mean triglycerides, LDL-C and apo B levels were found with apo E3/4, and lower mean levels of HDL-C i.e. apo A-I than in other analyzed genotypes. Greater mean of total/HDL ratio and lower levels of apo A-II were seen with E2/4. Serum lipoprotein Lp (a) concentration was higher in women with genotypes E3/3. Apo E concentration was the lowest with genotypes E4/4, i.e. the highest with E2/3. Serum total cholesterol tended to be higher in women with genotypes E4/4. Genotype E3/4 is connected with the highest concentrations of (X +/- SD) triglycerides (1.74 +/- 0.78), LDL (4.28 +/- 1.88), apo B (1.03 +/- 0.32) and with the lowest concentrations of HDL cholesterol (1.11 +/- 0.21) in the relation to the other analyzed genotypes. This group of women could possibly represent high risk women for CHD. Genotype E3/3 is associated with the highest concentration of independent genetic risk marker for CHD, lipoprotein Lp (a) (0.19 +/- 0.27). The genotype E4/4 has the highest concentration of total cholesterol (5.93 +/- 1.01), and has to be taken in account for risk evaluation in women. High level of apo E (0.11 +/- 0.05) and low level of apo A-I (1.80 +/- 0.44) were associated with E2/3 genotypes. The significance of E3/4 with the high total/HDL ratio (5.52 +/- 2.21) and low apo A-II (0.53 +/- 0.09) is important indicator, because total/HDL cholesterol ratio represents independent Established Risk Factor (ERF) for CHD. Apolipoprotein E genotypes as genetic markers and investigation of serum metabolic risk markers appear to be important in view for further evaluation of high risk women for CHD in our population.     

Apolipoprotein B-32: a new truncated mutant of human apolipoprotein B capable of forming particles in the low density lipoprotein range.

We have identified a new species of apolipoprotein (apo) B in an individual with heterozygous hypobetalipoproteinemia. The new apo B (apo B-32) is the result of a single point mutation (1450 Gln----Stop) in the apo B gene that prevents full length translation. Apo B-32 is predicted to contain the 1449 amino-terminal amino acids of apo B-100 and is associated with a markedly decreased low density lipoprotein (LDL) cholesterol level. The density distribution of apo B-32 in the plasma lipoproteins makes it unique amongst other truncated apo B species. Normally, apo B-100 is found in both very low density lipoprotein (VLDL) and LDL particles. However, the majority of the apo B-32 protein was found in the high density lipoprotein (HDL) and lipoprotein-deplete (d greater than 1.21 g/ml) fractions, suggesting that it was mainly assembled into abnormally dense lipoprotein particles. A small amount of apo B-32 was also found in the LDL, making it the shortest known apo B variant capable of forming particles in this density range. Apo B-32 was undetected in VLDL. The apo B-32 mutation further defines the minimum length of the apo B protein that is required for the assembly of LDL.     

Low-density-lipoprotein receptors in different rabbit liver cells.

Receptor-dependent uptake mechanisms for low-density lipoprotein (LDL) were studied in rabbit liver parenchymal and non-parenchymal cells. Hybridization studies with a cDNA probe revealed that mRNA for the apo (apolipoprotein) B,E receptor was present in endothelial and Kupffer cells as well as in parenchymal cells. By ligand-blotting experiments we showed that apo B,E-receptor protein was present in both parenchymal and non-parenchymal cells. Studies of binding of homologous LDL in cultured rabbit parenchymal cells suggested that about 63% of the specific LDL binding was mediated via the apo B,E receptor. Approx. 47% of the specific LDL binding was dependent on Ca2+, suggesting that specific Ca2+-dependent as well as Ca2+-independent LDL-binding sites exist in liver parenchymal cells. Methylated LDL bound to the parenchymal cells in a saturable manner. Taken together, our results showed that apo B,E receptors are present in rabbit liver endothelial and Kupffer cells as well as in the parenchymal cells, and that an additional saturable binding activity for LDL may exist on rabbit liver parenchymal cells. This binding activity was not inhibited by EGTA or reductive methylation of lysine residues in apo B. LDL degradation in parenchymal cells was mainly mediated via the apo B,E receptor.     

Unmasking of Type III Hyperlipoproteinemia by Hypothyroidism: A Dramatic Illustration of Altered Lipoprotein Metabolism in a Postpartum Woman

ObjectiveTo illustrate the potential abnormalities in lipoprotein metabolism associated with type III hyperlipoproteinemia and the modulation of their clinical expression by thyroid hormone and estrogenic status.MethodsAn illustrative case, with associated clinical and laboratory data, is presented, and relevant clinical and pathophysiologic studies from the literature are reviewed.ResultsA 35-year-old woman, at 7 months after delivery of her first child, presented to her family physician with a complaint of painful eruptions on the palms of her hands. On evaluation, she was found to have new hypothyroidism and severe hypertriglyceridemia (> 1,569 mg/dL). Thyroxine replacement was initiated, and she was referred to the lipid clinic. When seen in the lipid clinic shortly thereafter, her triglyceride level had normalized, but her low-density lipoprotein (LDL) fraction was strikingly elevated (representing a combination of elevated intermediate-density lipoprotein and LDL cholesterol). On physical examination, palmar xanthomas were noted, suggestive of type III hyperlipoproteinemia. This diagnosis was further supported by homozygosity at the apolipoprotein E (apo E) gene locus for the apo E2 allele implicated in this condition. Ultimately, with attainment of euthyroidism in the subsequent weeks, the lipid profile normalized, with the LDL cholesterol concentration particularly reduced at 55 mg/dL.Conclusion: Clinical expression of type III hyperlipoproteinemia necessitates interaction between an underlying genetic defect of lipoprotein metabolism (apo E2 homozygosity) and a secondary metabolic insult such as, in the current case, hypothyroidism and possibly breast-feeding-mediated hypoestrogenemia. As such, in patients with type III hyperlipoproteinemia, it is essential to search for exacerbating factors, particularly because the amelioration of such factors may rectify the effects of the underlying dyslipidemia. (Endocr Pract. 2005;11:394-398)     

Effects of apolipoprotein B-100 on the metabolism of a lipid microemulsion model in rats

In previous studies, it was shown that lipid microemulsions resembling LDL (LDE) but not containing protein, acquire apolipoprotein E when injected into the bloodstream and bind to LDL receptors (LDLR) using this protein as ligand. Aiming to evaluate the effects of apolipoprotein (apo) B-100 on the catabolism of these microemulsions, LDE with incorporated apo B-100 (LDE-apoB) and native LDL, all labeled with radioactive lipids were studied after intraarterial injection into Wistar rats. Plasma decay curves of the labels were determined in samples collected over 10 h and tissue uptake was assayed from organs excised from the animals sacrificed 24 h after injection. LDE-apo B had a fractional clearance rate (FCR) similar to native LDL (0.40 and 0.33, respectively) but both had FCR pronouncedly smaller than LDE (0.56, P<0.01). Liver was the main uptake site for LDE, LDE-apoB, and native LDL, but LDE-apoB and native LDL had lower hepatic uptake rates than LDE. Pre-treatment of the rats with 17α-ethinylestradiol, known to upregulate LDLR, accelerated the removal from plasma of both LDE and LDE-apoB, but the effect was greater upon LDE than LDE-apoB. These differences in metabolic behavior documented in vivo can be interpreted by the lower affinity of LDLR for apo B-100 than for apo E, demonstrated in in vitro studies. Therefore, our study shows in vivo that, in comparison with apo E, apo B is a less efficient ligand to remove lipid particles such as microemulsions or lipoproteins from the intravascular compartment.     

Site-directed mutagenesis of an apolipoprotein E mutant, apo E5(Glu3----Lys) and its binding to low density lipoprotein receptors.

Apo E5(Glu3----Lys) is a naturally occurring apolipoprotein E (apo E) mutant found in patients with hyperlipoproteinemia and atherosclerosis. It has been shown to have a high affinity for low density lipoprotein (LDL) receptors. In this study, mutant apo E5 was produced by Chinese hamster ovary cells by means of an in vitro site-directed mutagenesis technique, and its LDL receptor binding activity was assessed. The apo E5 obtained from gene expression bound more readily to the LDL receptor than did plasma apo E3. The concentrations required for 50% competitive binding of 125I-labeled LDL to the LDL receptors were 58.9 ng/ml for plasma apo E3 and 25.7 ng/ml for the expressed apo E5. The expressed apo E5 displayed 229% normal binding. This result is highly consistent with that obtained with plasma apo E5, which showed 217% normal binding. Although the experimental apo E isoproteins contained more sialic acid than plasma apo E, the extent of sialylation had no effect on the receptor binding of apo E.     

Effects of insulin deficiency on lipoproteins and their hepatic receptors in rico rats

The present study was designed to examine the effect of streptozotocin (STZ)-induced diabetes on the plasma lipoprotein profile and hepatic expression of the LDL receptor and HDL binding protein (HB2) in hypercholesterolemic Rico rats. The plasma level of HDL1 (density range 1.040–1.063), which is particularly high in this rat strain, decreased (−25 %) 28 d after STZ administration (50 mg/kg). In contrast, the treatment increased (+54 %) the plasma concentration of HDL2 (density range 1.063–1.210). These variations in the lipoprotein concentrations were associated with inverse changes in the hepatic protein levels of the LDL receptor (+118 %) and HB2 (−46 %). These results suggest that the hepatic expression of HB2, a putative HDL receptor, can influence the plasma level of apo Al-rich HDL as has already been shown for the LDL receptor for apo B/E containing lipoproteins.     

Responses of plasma apolipoproteins to gonadectomy and androgen substitution in male rats

To obtain information on testosterone effects on plasma apolipoproteins, the amount and composition of apo-proteins in lipoproteins of 5 density classes (VLDL, LDL, HDL2b, HDL2a, HDL3) was estimated in 3 groups of adult male rats: normal control rats, castrated rats, and rats injected daily with testosterone propionate (200 micrograms/day) for one week after castration. Apoproteins were separated by sodium dodecylsulfate polyacrylamide gel electrophoresis after ultracentrifugation of plasma, and determined colorimetrically. Total amount of apoprotein carried in LDL (d = 1.006-1.063 g/ml) and HDL2b (d = 1.063-1.100 g/ml) was higher in castrated than in control rats, but was not significantly different from controls in testosterone substituted rats. LDL apo B and HDL2b apo E were higher in castrated than in normal rats; control levels were observed in androgen substituted rats. Except for a greatly increased relative amount of HDL2b apo E, and a decreased percentage of HDL2b apo A-I in castrated rats, there were no significant alterations by castration of apoprotein composition of the lipoproteins. The results raise the question whether the androgenic state might affect processes related to the effects of plasma LDL apo B and HDL apo E.     

Cellular metabolism of human plasma intermediate-density lipoprotein (IDL)

The cellular metabolism of human plasma intermediate-density lipoprotein (IDL) was investigated in cultured human skin fibroblasts and hepG-2 cell in the absence and presence of exogenous recombinant or plasmatic apo E-3. IDL (d 1.006-1.019 g/ml) and LDL (d 1.019-1.063 g/ml) were prepared by centrifugation from the plasma of apo E-3/3 or 4/3 normolipidemic human subjects. Without added apo E-3, IDL binding and cell association are similar or slightly reduced while their degradation is one third to one half. This results in degradation to binding ratios for IDL that are half those for LDL. Exogenous apo E-3 enhances binding, association and degradation of IDL by 50-150%, but the degradation to binding ratio remains low. Exogenous apo E-3 also increased the ability of IDL but not LDL, to down-regulate the incorporation of [14C]acetate to sterol by the cells. The optimal concentration of apo E-3 is 4 micrograms protein/10 micrograms IDL protein and at that concentration appreciable amounts of the apo E are found associated with the lipoprotein. Apo E-2 has no effect on the cellular metabolism of IDL and apo E-3 is not effective in receptor-negative human fibroblasts. Monoclonal antibodies that block apo E binding to B,E (LDL) receptor (1D7) abolish the cellular metabolism of IDL while antibodies against B-100 (4G3) are ineffective. In competitive binding experiments, IDL is slightly more effective than LDL in displacing 125I-LDL from receptors in hepG-2 cells and appreciably more effective than LDL when tested against 125I-IDL. Apo E-3 increases the capacity of IDL to compete with either 125I-LDL or 125I-IDL. Addition of apo E-3 also increases the binding affinity of IDL to hepG-2 receptors, with Kd values of 2.50, 0.93 micrograms protein/ml, respectively. The study demonstrates the essential role that functional apo E molecules play in the interaction of human IDL with cellular receptors. Yet, in spite of presence of apo E in IDL (2-3 molecules/particle) and enrichment of IDL with apo E-3 (to 4-5 molecules/particle) the proteolytic degradation of the lipoprotein by specific cellular receptor is similar to LDL.     

Partial apolipoprotein E-beta-galactosidase fusion protein expressed in Escherichia coli retains binding activity to the LDL(B/E) receptor

A partial rat apo E-beta-galactosidase fusion protein was produced in Escherichia coli Y1089 infected with recombinant lambda GT11 obtained by immunoscreening of a rat liver cDNA library with an anti-rat LDL antiserum. Partial cDNA overlapped the apo E mRNA sequence coding for apo E binding domain towards the LDL(B/E) receptor up to codon for Arg-139. Fusion protein specifically bound to human fibroblasts. The high-affinity component exhibited a Kd of 5 x 10(-8) M and 4.1 x 10(5) sites per cell. Fusion protein binding to fibroblasts was mediated by their apo E moiety and not by beta-galactosidase since: (1) specific binding of fusion protein was competed out by human LDL; (2) beta-galactosidase did not compete with fusion protein binding; and (3) human fibroblasts from a patient with familial hypercholesterolemia, deficient in LDL(B/E) receptor, bound fusion protein 10-times lower than control fibroblasts. It was demonstrated that partial fusion protein retained the functional activity of the native apo E. However, compared to full-length native or engineered apo E, fusion protein was able to bind fibroblasts without being complexed with phospholipids. Fusion proteins might be a useful tool for studying the functional efficiency of the LDL(B/E) receptor and for mapping residues and domains involved in the binding process.     

Candidate-gene studies of the atherogenic lipoprotein phenotype: a sib-pair linkage analysis of DZ women twins.

There is a growing body of evidence supporting the roles of small, dense LDL and plasma triglyceride (TG), both features of the atherogenic lipoprotein phenotype, as risk factors for coronary heart disease. Although family studies and twin studies have demonstrated genetic influences on these risk factors, the specific genes involved remain to be determined definitively. The purpose of this study was to investigate genetic linkage between LDL size, TG, and related atherogenic lipoproteins and candidate genes known to be involved in lipid metabolism. The linkage analysis was based on a sample of 126 DZ women twin pairs, which avoids the potentially confounding effects of both age and gender, by use of a quantitative sib-pair linkage-analysis approach. Eight candidate genes were examined, including those for microsomal TG-transfer protein (MTP), hepatic lipase, hormone-sensitive lipase, apolipoprotein (apo) B, apo CIII, apo E, insulin receptor, and LDL receptor. The analysis suggested genetic linkage between markers for the apo B gene and LDL size, plasma levels of TG, of HDL cholesterol, and of apo B, all features of the atherogenic lipoprotein phenotype. Furthermore, evidence for linkage was maintained when the analysis was limited to women with a major LDL-subclass diameter >255 A, indicating that the apo B gene may influence LDL heterogeneity in the intermediate-to-large size range. In addition, linkage was found between the MTP gene and TG, among all the women. These findings add to the growing evidence for genetic influences on the atherogenic lipoprotein phenotype and its role in genetic susceptibility to atherosclerosis.     

Linkage analysis of the genetic determinants of high density lipoprotein concentrations and composition: evidence for involvement of the apolipoprotein A-II and cholesteryl ester transfer protein loci

We have tested for evidence of linkage between the genetic loci determining concentrations and composition of plasma high density lipoproteins (HDL) with the genes for the major apolipoproteins and enzymes participating in lipoprotein metabolism. These genes include those encoding various apolipoproteins (apo), including apoA-I, apoA-II, apoA-IV, apoB, apoC-I, apoC-II, apoC-III, apoE, and apo(a), cholesteryl ester transfer protein (CETP), HDL-binding protein, lipoprotein lipase, and the low density lipoprotein (LDL) receptor. Polymorphisms of these genes, and nearby highly polymorphic simple sequence repeat markers, were examined by quantitative sib-pair linkage analysis in 30 coronary artery disease families consisting of a total of 366 individuals. Evidence for linkage was observed between a marker locus D16S313 linked to the CETP locus and a locus determining plasma HDL-cholesterol concentration (P = 0.002), and the genetic locus for apoA-II and a locus determining the levels of the major apolipoproteins of HDL, apoA-I and apoA-II (P = 0.009 and 0.02, respectively). HDL level was also influenced by the variation at the apo(a) locus on chromosome 6 (P = 0.02). Thus, these data indicate the simultaneous involvement of at least two different genetic loci in the determination of the levels of HDL and its associated lipoproteins.     

The action of defined oxygen-centred free radicals on human low-density lipoprotein.

The effects of defined oxygen-centred free radicals on human low-density lipoprotein (LDL) structure and receptor affinity are discussed in relation to the mechanisms of cell-mediated oxidative modification of LDL. Both hydroxyl (OH.) and hydroperoxyl (HO2.) radicals caused depletion of endogenous alpha-tocopherol and formation of hydroperoxides. Superoxide (O2-.) radicals produced only very limited oxidation, but could potentiate oxidation stimulated by the addition of Cu2+. All these radicals enhanced the net negative charge of intact LDL and induced fragmentation of apolipoprotein B-100 (apo B). OH. also caused cross-linking of apo B. Radical attack decreased the affinity of LDL for the fibroblast apo B/E receptor, but did not enhance its endocytosis by mouse macrophages.     

Genetic evidence that the putative receptor binding domain of apolipoprotein B (residues 3130 to 3630) is not the only region of the protein involved in interaction with the low density lipoprotein receptor

We have searched for sequence differences in the region of the apolipoprotein B (apo B) gene encoding amino acids 3130-3630 in eight individuals with reduced affinity of low density lipoprotein (LDL) for the normal LDL-receptor. All individuals were hypercholesterolaemic and were selected either on the basis of reduced fractional catabolic rate (FCR) of autologous LDL or substantially reduced binding of their LDL to normal LDL-receptors determined by an in vitro cell growth assay using the U937 macrophage-like cell line. Segments of the apo B gene were amplified by the polymerase chain reaction. Using a combination of cloning and sequencing the amplified fragment, together with chemical cleavage mismatch analysis, no sequence differences were identified in this region of the gene. We therefore conclude that variation outside the region of the apo B gene that codes for amino acids 3130-3630 must be responsible for the reduced LDL clearance in these patients.     

High frequency of the apo ɛ4 allele in Khoi San from South Africa

Variation at the apolipoprotein E (apo E) gene locus affects cholesterol concentrations, the risk for atherosclerosis and Alzheimer disease (AD), and is associated with longevity in Caucasians. We have determined apo E gene frequencies and effects on cholesterol levels in Khoi San (Bushmen) from South Africa. The frequency of the apo 4 allele (0.37), which confers dose-dependent susceptibility to atherosclerosis and AD in Caucasians, was twice as high, and apo E4 homozygotes were 3–5 fold more frequent in the Khoi San ( 10%) compared with Caucasians (2%–3%). No significant effect of apo E variation on cholesterol concentration was noted in this non-Westernized population with low plasma cholesterol (mean cholesterol 149 mg/dl). This suggests that Bushmen carry a heavy genetic burden for these late-onset disorders if exposed to a Western lifestyle.     

Apolipoprotein E polymorphism in the Netherlands and its effect on plasma lipid and apolipoprotein levels

Summary By isoelectric focusing of delipidated sera followed by immunoblotting we studied the apolipoprotein (apo) E polymorphism in 2018 randomly selected 35-years-old males from three different areas in the Netherlands. Comparison of the APOE allele (E^*2, E^*3, and E^*4) frequencies estimated in this study with those reported for several other population samples showed that there are marked differences between the Dutch population and the populations of Japan, New Zealand, Finland, and the United States. These differences in APOE allele frequencies appeared to be mainly due to differences in frequencies of the E^*2 allele (decreased in Japan and Finland; increased in New Zealand) and the E^*4 allele (increased in Finland; decreased in Japan and the United States). No difference in APOE allele frequencies was found between the Dutch population and the populations of West Germany and Scotland. Measurements of plasma cholesterol and apo B and E concentrations showed that the E^*4 allele is associated with elevated plasma cholesterol and apo B levels and with decreased apo E concentrations, whereas the opposite is true for the E^*2 allele. In the Dutch population, the sum of average allelic effects of the common APOE alleles on plasma cholesterol and apo B levels is 6.8% and 14.2%, respectively, of the total population mean. The total average allelic effect on plasma apo E concentrations was more pronounced (50.1%), suggesting that the APOE alleles primarily affect apo E concentrations rather than plasma cholesterol and apo B levels. This hypothesis is sustained by the observation that for plasma apo E levels the genetic variance associated with the APOE gene locus contributed about 18% to the total phenotypic variance. For plasma cholesterol and apo B this contribution was only 1.4% and 2.3% and is relatively low as compared with that reported for other population samples.