Effects of polymorphisms in apolipoproteins E, A-IV, and H on quantitative traits related to risk for cardiovascular disease

Genome-wide analysis identifies novel loci influencing plasma apolipoprotein E concentration and Alzheimer's disease risk

The APOE 2/3/4 polymorphism is the greatest genetic risk factor for Alzheimer's disease (AD). This polymorphism is also associated with variation in plasma ApoE level; while APOE*4 lowers, APOE*2 increases ApoE level. Lower plasma ApoE level has also been suggested to be a risk factor for incident dementia. To our knowledge, no large genome-wide association study (GWAS) has been reported on plasma ApoE level. This study aimed to identify new genetic variants affecting plasma ApoE level as well as to test if baseline ApoE level is associated with cognitive function and incident dementia in a longitudinally followed cohort of the Ginkgo Evaluation of Memory (GEM) study. Baseline plasma ApoE concentration was measured in 3031 participants (95.4% European Americans (EAs)). GWAS analysis was performed on 2580 self-identified EAs where both genotype and plasma ApoE data were available. Lower ApoE concentration was associated with worse cognitive function, but not with incident dementia. As expected, the risk for AD increased from E2/2 through to E4/4 genotypes (P for trend = 4.8E-75). In addition to confirming the expected and opposite associations of APOE*2 (P = 4.73E-79) and APOE*4 (P = 8.73E-12) with ApoE level, GWAS analysis revealed nine additional independent signals in the APOE region, and together they explained about 22% of the variance in plasma ApoE level. We also identified seven new loci on chromosomes 1, 4, 5, 7, 11, 12 and 20 (P range = 5.49E-08 to 5.36E-10) that explained about 9% of the variance in ApoE level. Plasma ApoE level-associated independent variants, especially in the APOE region, were also associated with AD risk and amyloid deposition in the brain, indicating that genetically determined ApoE level variation may be a risk factor for developing AD. These results improve our understanding of the genetic determinants of plasma ApoE level and their potential value in affecting AD risk.

Discovery and refinement of loci associated with lipid levels

Levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides and total cholesterol are heritable, modifiable risk factors for coronary artery disease. To identify new loci and refine known loci influencing these lipids, we examined 188,577 individuals using genome-wide and custom genotyping arrays. We identify and annotate 157 loci associated with lipid levels at P < 5 × 10(-8), including 62 loci not previously associated with lipid levels in humans. Using dense genotyping in individuals of European, East Asian, South Asian and African ancestry, we narrow association signals in 12 loci. We find that loci associated with blood lipid levels are often associated with cardiovascular and metabolic traits, including coronary artery disease, type 2 diabetes, blood pressure, waist-hip ratio and body mass index. Our results demonstrate the value of using genetic data from individuals of diverse ancestry and provide insights into the biological mechanisms regulating blood lipids to guide future genetic, biological and therapeutic research.

Apolipoprotein E-ε4 polymorphism and cognitive dysfunction after carotid endarterectomy

Approximately 25% of patients undergoing carotid endarterectomy (CEA) exhibit cognitive dysfunction (CD) 1 day and 1 month after CEA. The apolipoprotein E (apoE)-ε4 polymorphism has been previously identified as a robust independent risk factor for CD 1 month after CEA. We aimed to determine whether the apoE-ε4 polymorphism is also an independent risk factor for CD as early as 1 day after CEA and to confirm the previous findings at 1 month. Patients undergoing elective CEA (n=411) were enrolled with written informed consent in this follow-up observational study. CD was evaluated via an extensive neuropsychometric battery. apoE-ε4 carriers exhibited significantly more CD 1 day (30.1% versus 17.9%, p=0.01) and 1 month (25.7% versus 9.8%, p=0.001) after CEA compared to non-carriers. Multivariate regression models were generated to determine independent predictors of CD. At 1 day, apoE-ε4 was significantly associated with higher risk of CD (odds ratio [OR]: 2.24 [95% confidence interval 1.29-3.84], p=0.004), while statin use was significantly associated with lower risk (OR: 0.40 [0.24-0.67], p<0.001). At 1 month, apoE-ε4 was significantly associated with higher risk of CD (OR: 3.14 [1.53-6.38], p=0.002), while symptomatic status was significantly associated with lower risk (OR: 0.45 [0.20-0.94], p=0.03). The apoE-ε4 polymorphism is an independent risk factor for CD as early as 1 day after CEA and is confirmed to be an independent risk factor for CD at 1 month as well.

Context-dependent associations between variation in risk of ischemic heart disease and variation in the 5' promoter region of the apolipoprotein E gene in Danish women

OBJECTIVE

Variations in the noncoding single-nucleotide polymorphisms (SNPs) at positions 560 and 832 in the 5' promoter region of the apolipoprotein E gene define genotypes that distinguish between high and low concentrations of plasma total and high-density lipoprotein cholesterol and triglycerides. We addressed whether these genotypes improve the prediction of ischemic heart disease (IHD) in subsamples of individuals defined by traditional risk factors and the genotypes defined by the epsilon(2), epsilon(3), and epsilon(4) alleles in exon 4 of the apolipoprotein E gene.

METHODS AND RESULTS

In a sample of 3686 female and 2772 male participants of the Copenhagen City Heart Study who were free of IHD events, 576 individuals (257 women, 7.0% and 319 men, 11.5%) were diagnosed as having developed IHD in 6.5 years of follow-up. Using a stepwise Patient Rule-Induction Method modeling strategy that acknowledges the complex pathobiology of IHD, we identified a subsample of 764 elderly women (> or =65 years) with hypertriglyceridemia who had a history of smoking, a history of hypertension, or a history of both in which the A(560)T(832)/A(560)T(832) and A(560)T(832)/A(560)G(832) 5' 2-SNP genotypes had a higher cumulative incidence of IHD (172/1000) compared to the incidence of 70/1000 in the total sample of women.

CONCLUSIONS

Our study validates that 5' apolipoprotein E genotypes improve the prediction of IHD and documents that the improvement is greatest in a subset defined by a particular combination of traditional risk factors in Copenhagen City Heart Study female participants. We discuss the use of these genotypes in medical risk assessment of IHD in the population represented by the Copenhagen City Heart Study.

Comprehensive evaluation of apolipoprotein H gene (APOH) variation identifies novel associations with measures of lipid metabolism in GENOA

Apolipoprotein H (apoH, also named beta-2 glycoprotein I) is found on several classes of lipoproteins, and is involved in the activation of lipoprotein lipase in lipid metabolism. We have comprehensively investigated the association of variation in the apoH gene (APOH) with lipid traits in hepatic cholesterol transport, dietary cholesterol transport (DCT), and reverse cholesterol transport (RCT). Our study population consisted of families from the Genetic Epidemiology Network of Arteriopathy multicenter study that include African Americans, Mexican Americans, and European Americans. We individually tested 36 single-nucleotide polymorphisms (SNPs) that span the APOH locus, including nonsynonymous variants that result in known apoH charge isoforms. In addition, we constructed haplotypes from SNPs in the 5' promoter region that comprise cis-acting regulatory elements, as well as haplotypes for multiple amino acid substitutions. We found point-wise significant associations of APOH variants with various lipid measures in the three racial groups. The strongest associations were found for DCT traits (triglyceride and apoE levels) in Mexican Americans with a nonsynonymous variant (SNP 14917, Cys306Gly) that may alter apoH protein folding in a region involved in phospholipid binding. In conclusion, family-based analyses of APOH variants have identified associations with measures of lipid metabolism in three American racial groups.

ESR1 polymorphism is associated with plasma lipid and apolipoprotein levels in Caucasians of the Rochester Family Heart Study

We evaluated six estrogen receptor 1 (ESR1) polymorphisms for association with ten plasma lipid and apolipoprotein traits in 1,847 individuals (941 females and 906 males) in the multi-generation Rochester Family Heart Study using a generalized estimating equation approach. Apolipoprotein A-I (apoA-I), apoA-II, and HDL-cholesterol (HDL-C) were associated with exon 4 rs1801132 (Pro325Pro) genotype (P = 0.0044, P = 0.0048, and P = 0.0035, respectively). Positive correlation between levels of apoA-I, apoA-II, and HDL-C and the number of G alleles was observed in females (P = 0.0120, P = 0.0032, and P = 0.0030), but not males (P > 0.05). Because few studies have evaluated the effect of ESR1 gene polymorphisms on lipid traits in children, we also stratified our sample at the age of 15 years. There was evidence of association between intron 1 single-nucleotide polymorphisms rs9322331 and rs9340799 and apoC-II, and triglycerides (TGs) in youths 15 years and younger. In youths, evidence of association between rs9322331 and rs9340799 and apoC-II was stronger in males (P = 0.0036 and P = 0.0124) than in females (P > 0.05), whereas evidence of association with TG was stronger in females (P = 0.0030 and P = 0.0024) than in males (P > 0.05). These findings suggest that ESR1 variation plays an age- and sex-dependent role in determining plasma lipid and apolipoprotein levels.

Biomarker analysis by fluorokine multianalyte profiling distinguishes patients requiring intervention from patients with long-term quiescent coronary artery disease: a potential approach to identify atherosclerotic disease progression

BACKGROUND

The study rationale was to compare the biomarker profile of metalloproteinases (MMPs) and inflammation markers (IMs) in patients requiring revascularization with that of patients with long-term, clinically quiescent coronary artery disease (CAD).

METHODS

Seventy-eight patients with symptomatic CAD (S-CAD) (7 patients with myocardial infarction and 71 patients with stable angina) and 67 patients with asymptomatic CAD (A-CAD) were enrolled. Plasma samples were analyzed for MMPs, MMP inhibitors (MMPIs), IMs, coagulation factors, and apolipoproteins by use of the fluorokine multianalyte profiling assay.

RESULTS

Patients with S-CAD had markedly elevated levels of specific MMPs (MMP-2, MMP-9), MMPIs (alpha2-macroglobulin, tissue inhibitor of MMP 1), IMs (C-reactive protein; interleukin [IL] 8; IL-10, regulated upon activation, normal T-cell expressed and secreted [RANTES], endothelin, plasminogen activator inhibitor 1, and apolipoprotein C-III compared with patients with A-CAD (P < .005 for all measurements), whereas patients with A-CAD had significantly greater levels of MMP-3 and IL-1alpha compared with patients with S-CAD (P < or = .02 for both measurements).

CONCLUSIONS

A specific profile of MMPs, IMs, and other biomarkers distinguishes the patient with progressive coronary atherosclerosis culminating in either elective or emergent percutaneous coronary intervention from the patient with quiescent disease. The early implementation of a biomarker analysis may identify the patient at risk for plaque progression and refine the definition of "stable" angina.

Genetic architecture of common multifactorial diseases

The purpose of this paper is to foster a dialogue among those interested in the genetic analysis of common chronic diseases. The need for an alternative to the Cartesian-Mendelian research strategy is discussed. A biological model that considers an individual's health to be an emergent property of a complex adaptive system is presented. A review of the contribution of the gene coding for apolipoprotein E to the genetic architecture of measures of lipid metabolism documents that an individual's coronary artery health has all the features expected of a complex adaptive system. Suggestions for enhancing our ability to use genetic information to predict onset, progression and severity of disease are offered.

Polimorfismos genéticos: implicações na patogênese do carcinoma medular de tireóide

O carcinoma medular de tireóide (CMT) é uma neoplasia maligna rara, ocorrendo na forma esporádica ou hereditária. Mutações germinativas no proto-oncogene RET são responsáveis pelo CMT hereditário. No entanto, a maioria dos casos de CMT ocorre em indivíduos sem história familiar, na qual a patogênese da doença ainda é pouco compreendida. Os polimorfismos do gene RET são descritos na população geral assim como em pacientes com CMT. Embora estas variações alélicas aparentemente não confiram qualquer atividade transformadora no receptor RET, estudos sugerem que essas alterações genéticas podem modificar a suscetibilidade à doença e o fenótipo clínico em pacientes com CMT esporádico ou hereditário. Uma maior freqüência dos polimorfismos localizados nos exons 11 (G691S), 13 (L769L), 14 (S836S) e 15 (S904) é descrita em pacientes com CMT provenientes de países americanos e europeus. Na presente revisão, analisamos criticamente os resultados obtidos nos diferentes estudos e descrevemos a freqüência dos polimorfismos do RET em pacientes brasileiros com CMT esporádico.

Contribution of regulatory and structural variations in APOE to predicting dyslipidemia

The objective of this study was to evaluate 1) whether non single nucleotide polymorphisms-coding (non-cSNP) in the apolipoprotein E gene (APOE) identified by resequencing studies contribute to statistically explaining dyslipidemia if variations in the two cSNPs in exon 4 that define the 2, 3, and 4 alleles are ignored, and 2) whether the contribution of these additional SNPs persists when variations in the cSNPs are considered. We used an ecological, multiple-population, data-mining strategy to identify single-SNP and two-SNP genotypes that distinguish between high and low levels of plasma lipids in three training samples, European-Americans from Rochester, MN, African-Americans from Jackson, MS, and Europeans from North Karelia, Finland. We found that a pair of SNPs located in the 5' region define genotypes A560T832/A560T832, A560T832/A560G832, and A560T832/T560T832, which distinguish between high and low levels of HDL-cholesterol (HDL-C), triglycerides (TG), and/or total cholesterol (T-C). The A560T832/- genotypes predicted high TG and high T-C in both genders in a large independent test sample from Copenhagen, Denmark. Prediction of high T-C in the Danish females was dependent on genotypes defined by the cSNPs. Our study suggests that both regulatory and structural variations should be considered when evaluating the utility of APOE for predicting dyslipidemia in the population at large.

Detection of a major gene effect for LDL peak particle diameter and association with apolipoprotein H gene haplotype

Low-density lipoprotein (LDL) size, a coronary heart disease risk factor, is influenced by both genetic and environmental factors. Results from the Quebec Family Study (QFS) revealed that the LDL peak particle diameter (LDL-PPD) aggregates in families with a heritability coefficient above 50% and is affected by a major quantitative trait locus on chromosome 17q (LOD=6.8). Complex segregation analyses have consistently demonstrated a major gene effect influencing LDL size. In the present study, we report a similar analysis in the QFS cohort, which suggests that a major gene explains 23% of the variance in age-body mass index and triglyceride-adjusted LDL-PPD. The most intuitive positional candidate gene on chromosome 17q is the apolipoprotein H gene. Direct sequencing of the promoter, coding regions, and exon-intron splicing boundaries of this gene revealed the presence of three missense mutations and two polymorphisms in the untranslated regions. Using family-based association tests, none of these variants was individually associated with LDL-PPD. However, analysis of the haplotypes constructed from the three missense mutations, suggested that one particular haplotype (frequency=20.9%) was associated with a significant increase in LDL-PPD trait values (p=0.046). Taken together, these results suggest the presence of a major gene effect influencing LDL-PPD and a positive association with a positional candidate gene located on chromosome 17q. Replication of the association between apolipoprotein H gene haplotype and LDL-PPD is required before reaching firm conclusion.

APOE-epsilon4 predisposes to cognitive dysfunction following uncomplicated carotid endarterectomy

BACKGROUND

Between 9% and 23% of patients undergoing otherwise uncomplicated carotid endarterectomy (CEA) develop subtle cognitive decline 1 month postoperatively. The APOE-epsilon4 allele has been associated with worse outcome following stroke.

OBJECTIVE

To investigate the ability of APOE-epsilon4 to predict post-CEA neurocognitive dysfunction.

METHODS

Seventy-five patients with CEA undergoing elective CEA were prospectively recruited in this nested cohort study and demographic variables were recorded. Patients were evaluated before and 1 month after surgery with a standard battery of five neuropsychological tests. APOE genotyping was performed by restriction fragment length polymorphism analysis in all patients. Neuropsychological deficits were identified by comparing changes (before to 1 month post-operation) in individual performance on the test battery. Logistic regression was performed for APOE-epsilon4 and previously identified risk factors.

RESULTS

Twelve of 75 (16%) CEA patients possessed the APOE-epsilon4 allele. Eight of 75 (11%) patients experienced neurocognitive dysfunction on postoperative day 30. One month post-CEA, APOE-epsilon4-positive patients were more likely to be cognitively injured (42%) than APOE-epsilon4-negative patients (5%) (p = 0.002). In multivariate analysis, the presence of the APOE-epsilon4 allele increased the risk of neurocognitive dysfunction at 1 month 62-fold (62.28, 3.15 to 1229, p = 0.007). Diabetes (51.42, 1.94 to 1363, p = 0.02), and obesity (24.43, 1.41 to 422.9, p = 0.03) also predisposed to injury.

CONCLUSION

The APOE-epsilon4 allele is a robust independent predictor of neurocognitive decline 1 month following CEA.

Apolipoprotein E e4 Allele and Neurobehavioral Status After On-Pump Coronary Artery Bypass Grafting

Abstract Background and Aim: The presence of apolipoprotein E epsilon4 allele is being considered as a risk factor for cognitive decline after cardiac surgery. We sought the effect of apolipoprotein E epsilon4 allele on neurobehavioral status after on-pump coronary artery bypass grafting.

METHODS

Prior to the operation, neurologic examination and neurobehavioral cognitive status test (COGNISTAT) were performed. Both procedures were repeated on the day of discharge and 3 months after surgery. Apolipoprotein E epsilon4 allele positive and apolipoprotein E epsilon4 allele negative patients' performance on COGNISTAT were compared.

RESULTS

There was no statistically significant demographic and operative data difference between two groups. No neurological impairment was observed on examinations. There was no statistically significant neurocognitive decline difference between two groups' postoperative performances.

CONCLUSIONS

It seems that apolipoprotein E epsilon4 allele may not affect neurobehavioral status in the intermediate period after on-pump coronary artery bypass grafting.

Association of apo A-IV 360 (Gln → His) polymorphism with plasma lipids and lipoproteins: the Framingham Offspring Study

The effect of a common apolipoprotein (apo) A-IV polymorphism (substitution of histidine for glutamine at position 360) on plasma lipid, lipoprotein cholesterol and lipoprotein(a) (Lp(a)) levels, and on low-density lipoprotein (LDL) particle size was examined by genotyping in 2322 Caucasian men and women (mean age: 48.9+/-10.1 years) participating in the Framingham Offspring Study (FOS). The relative frequencies of the apo A-IV-Gln (apo A-IV-1) and the apo A-IV-His (apo A-IV-2) alleles were 0.932 and 0.068, respectively, and were in Hardy-Weinberg equilibrium. No effect of the apo A-IV-2 genotype was observed on plasma triglyceride, total and lipoprotein cholesterol, and LDL particle size in either men or women after adjustment for age and body mass index. To avoid a possible interaction between the apo E genotype and the apo A-IV genotype, subgroup analyses were undertaken in 1,414 male and female subjects with the apo E3/3 genotype. Among women in this group there was a significant effect of the apo A-IV-2 allele on triglyceride levels (p=0.046). This effect was no longer significant after adjustment for age and BMI (p=0.074). No significant allele effect on other lipoprotein levels, including Lp(a), was noted in apo E3/3 men or women. We have also conducted a meta-analysis of our own data and of other studies found in the literature, indicating a significant lowering effect of apo A-IV-2 on plasma triglycerides, but no effects on other parameters. In conclusion, the apo A-IV-2 allele is associated with a modest reduction in plasma triglyceride levels in the general population.

Gender- and age-specific contributions of additional DNA sequence variation in the 5' regulatory region of the APOE gene to prediction of measures of lipid metabolism

In the present study of 9,000 individuals representative of the general population, we have considered whether the addition of common single nucleotide polymorphisms (SNPs) in the promoter region of Apolipoprotein E (APOE) improve the statistical explanation of variation in lipid traits and test the hypothesis that the estimated genotype effects are independent of factors indexed by gender and age. To address these questions, we have asked, for each gender and for each 20-year age strata (young: 20-39 years; middle-aged: 40-59 years; old: 60-79 years; very old: 80-100 years), how much trait variation is associated with the traditional epsilon2, epsilon3, and epsilon4 allelic variations defined by the g.2059T --> C and g.2197C --> T SNPs in the fourth exon of the APOE gene, and how much additional trait variation is associated with genotypes defined by combining the g.2059T --> C and g.2197C --> T SNPs with one, two, or three promoter SNPs. Our study demonstrates that the pleiotropic effects of genotype variation defined by the traditional epsilon2, epsilon3, and epsilon4 alleles on five plasma measures of lipid metabolism manifest differently in women and men and change significantly during the life cycle for high-density lipoprotein cholesterol in women. Multi-site genotypes defined by adding SNPs located in the 5' promoter region to the traditional g.2059T --> C and g.2197C --> T SNPs doubled the estimate of genetic variance of high-density lipoprotein and apolipoprotein Al in middle-aged females.

APOA5 polymorphisms influence plasma triglycerides in young, healthy African Americans and whites of the CARDIA Study

Genetic variation in the apolipoprotein A-V gene (APOA5) has been associated with variation in plasma triglyceride (TG) levels in African American and white females and males older than 40 years and/or at increased risk of coronary artery disease. We have examined whether plasma TG levels are associated with 16 APOA5 polymorphisms in young (18-30 years) African American (1,075 females and 783 males) and white (1,041 females and 932 males) individuals of the Coronary Artery Risk Development in Young Adults (CARDIA) Study selected without regard to health. Plasma TG was significantly (P < 0.01) associated with markers 27376 and 28837 (-3A/G) in both white females and males, with 27709 (-1131T/C) and 29085 in white males, with 29009 (S19W) in African American females and white males, and with 30966 in African American females. No statistically significant associations were observed in African American males. These six single-nucleotide polymorphisms individually accounted for 0-0.78% of lnTG variation among white females, 0-2.46% among white males, and 0-0.69% among African American females. The results of our study suggest a small but replicable context-dependent influence of the APOA5 gene region on plasma TG levels in young, healthy individuals.

Evidence for Non-additive Influence of Single Nucleotide Polymorphisms within the Apolipoprotein E Gene

We analyzed 13 single nucleotide polymorphisms (SNPs) within the apolipoprotein E (APOE) gene, to identify pairs of SNPs that interact in a non-additive manner to influence genotypic mean levels of the ApoE protein in blood. An overparameterized general linear model of two-SNP genotype means was applied to data from 456 female and 398 male unrelated European Americans from Rochester, MN, USA. We found statistically significant evidence for non-additivity between SNPs within the male sample, but not within the female sample. We observed nine pairs of SNPs with evidence of non-additivity at the alpha=0.05 level of statistical significance within the male sample, when approximately three were expected by chance. Five of the nine pairs involved three SNPs (560, 624 and 1163) that did not have a statistically significant influence when considered separately in a single-site analysis. Three of the nine pairs involving four SNPs (832, 1998, 3937 and 4951) showed significant evidence for non-additivity in at least one of two other male samples from Jackson, MS, USA and North Karelia, Finland. Although all four of these SNPs had a statistically significant influence in Rochester when considered separately, only SNP 3937 gave a significant result in the other male samples. The four SNPs are located in the promoter, intronic and exonic regions, and 3' to the polyadenylation signal in the APOE gene. Our study suggests that analyses that only consider SNPs located in exons and ignore contexts such as those indexed by gender and population, and disregard non-additivity of SNP effects, may inappropriately model the contribution of a gene to the genetic architecture of a trait that has a complex multifactorial etiology.

Caliban's heritance and the genetics of neuronal aging

Although current research on brain aging is dominated by Alzheimer's disease (AD), many other brain changes arise during middle age in humans and in rodent models that are independent of AD-like neurodegeneration. Differences and continuities between normal and pathological aspects of neuronal aging reveal the relative contributions and interactions of genetic and environmental factors. Apolipoprotein E alleles might be prototypes for genetic polymorphisms associated with functional changes that arise during middle age. Mice are valuable models for these aspects of aging because most genotypes show little neurodegeneration, and none accumulate beta-amyloid unless human transgenes are introduced. As further human genes are found to modify normal and pathological neuronal aging, this zoo of aging-animal variants will facilitate analysis both of pathways of age-related neuronal dysfunction and of environmental influences on these pathways.

Heritability of C-reactive protein and association with apolipoprotein E genotypes in Japanese Americans

Numerous studies have demonstrated that increased C-reactive protein (CRP) levels predict coronary heart disease, stroke, peripheral vascular disease, and diabetes, and are associated with features of the metabolic syndrome. Only three previous studies have investigated the heritability of CRP levels, primarily in samples of Caucasian families. The purpose of the present study was to estimate the magnitude of genetic influences on CRP levels, and to examine potential associations between variation in the APOE gene and CRP levels, using a sample of 562 individual Japanese Americans from 68 extended kindreds. In general, correlation coefficients between first-degree relatives for CRP were approximately 0.2, and spouse correlations did not differ from zero, consistent with genetic influences. Heritability estimates were approximately 0.3 (p < 0.01), even with adjustment for factors known to influence CRP levels. A significant relationship was seen between unadjusted CRP levels and APOE genotypes (p = 0.02), with the highest mean CRP level among epsilon2 carriers (1.20 mg/L), and nearly the same mean levels among epsilon3/epsilon3 subjects and epsilon4 carriers (0.72 and 0.74 mg/L, respectively). However, this relationship was diminished with adjustment for covariates (p = 0.07). These results demonstrate the presence of both genetic and environmental effects on CRP levels among Asian Americans, and additional studies are needed to determine if the APOE gene contributes to these genetic influences.

Tree scanning: a method for using haplotype trees in phenotype/genotype association studies

We use evolutionary trees of haplotypes to study phenotypic associations by exhaustively examining all possible biallelic partitions of the tree, a technique we call tree scanning. If the first scan detects significant associations, additional rounds of tree scanning are used to partition the tree into three or more allelic classes. Two worked examples are presented. The first is a reanalysis of associations between haplotypes at the Alcohol Dehydrogenase locus in Drosophila melanogaster that was previously analyzed using a nested clade analysis, a more complicated technique for using haplotype trees to detect phenotypic associations. Tree scanning and the nested clade analysis yield the same inferences when permutation testing is used with both approaches. The second example is an analysis of associations between variation in various lipid traits and genetic variation at the Apolipoprotein E (APOE) gene in three human populations. Tree scanning successfully identified phenotypic associations expected from previous analyses. Tree scanning for the most part detected more associations and provided a better biological interpretative framework than single SNP analyses. We also show how prior information can be incorporated into the tree scan by starting with the traditional three electrophoretic alleles at APOE. Tree scanning detected genetically determined phenotypic heterogeneity within all three electrophoretic allelic classes. Overall, tree scanning is a simple, powerful, and flexible method for using haplotype trees to detect phenotype/genotype associations at candidate loci.

Apo A-IV: an update on regulation and physiologic functions

Apolipoprotein (apo) A-IV, first identified 28 years ago as a plasma lipoprotein moiety, is now known to participate in the regulation of various metabolic pathways. It is synthesized primarily in the enterocytes of the small intestine during fat absorption. After entry into the bloodstream, the 46-kDa glycoprotein apo A-IV appears associated with chylomicrons, high-density lipoproteins, and in the lipoprotein-free fraction. It has a role in lipid absorption, transport and metabolism, and may act as a post-prandial satiety signal, an anti-oxidant and a major factor in the prevention of atherosclerosis. After summarizing and discussing these functions for reader's comprehension, the current review focuses on the regulation of apo A-IV by nutrients, biliary components, drugs, hormones and gastrointestinal peptides. The understanding of the involved mechanisms that underline apo A-IV regulation may in the long run allow us to switch on its gene, which may confer multiple beneficial effects, including the protection from atherosclerosis.

Cladistic analysis of human apolipoprotein a4 polymorphisms in relation to quantitative plasma lipid risk factors of coronary heart disease

Genetic variation in several genes involved in lipid metabolism is known to affect population variation in quantitative lipid risk factor profiles for coronary heart disease (CHD). The apolipoprotein A-IV gene (APOA4) is one such candidate gene. We genotyped five polymorphisms in the APOA4 gene (codon 127, codon 130, codon347, codon 360 and 3' VNTR) and investigated their impact on plasma lipid trait levels in three populations comprising 604 U.S. non-Hispanic Whites (NHWs), 408 U.S. Hispanics and 708 Nigerian Blacks. Cladistic analysis was carried out to identify 5-site haplotypes that were associated with significant phenotypic differences in each population. The distribution of APOA4 genotypes was significantly different between ethnic groups. The Africans were monomorphic for two of the five sites (codons 130 and 360), but possess a unique 12 bp insertion that was not observed in NHWs and Hispanics. Due to linkage disequilibrium between the sites, only 6 haplotypes were observed in NHWs and Hispanics, and 4 in Africans. Several gender-and ethnic-specific associations between genotypes and plasma lipid traits were observed when single sites were used. Several haplotypes were identified by cladistic analysis that may carry functional mutations that affect plasma lipid trait levels.

Apolipoprotein E polymorphism affects carotid artery atherosclerosis in smoking hypertensive men

OBJECTIVE

Smoking is a risk factor for increased carotid artery intima-media thickness (IMT). The apolipoprotein E (apoE) 4 allele has been associated with cardiovascular diseases, but the role of apoE in regard to intima-media thickness (IMT) has remained controversial. The objective was to investigate whether there is some gene-environment interaction between smoking and apoE polymorphism. DESIGN Cross-sectional case-control study.

METHODS

IMTs of 511 hypertensive and control men were measured ultrasonographically and the apoE genotypes were determined. Genotypes with the 4 allele were pooled into one group and the genotypes without it into another.

RESULTS

A significant interaction between the 4 allele and smoking affecting IMT was observed among the hypertensive smokers, as assessed by analysis of covariance. The mean carotid IMT was significantly greater (1.01 versus 0.90 mm, P = 0.003) in the 4 carriers than in the subjects without 4 among the hypertensive smokers. The number of plaques was also significantly higher. No differences were found in the other subjects (hypertensive non-smokers or controls). Linear regression analysis indicated that the 4 allele was an independent determinant of IMT in the hypertensive smokers but not in the other subjects. The estimated average effect of the 4 allele on the mean IMT in the hypertensive smokers was 0.088 mm (P < 0.001). In the oldest age group, the interaction of smoking and 4 was also seen in the control subjects.

CONCLUSION

The findings suggest that the 4 carriers are particularly susceptible to the atherogenic effects of smoking. This interaction is particularly clear in hypertensive subjects.

Contributions of 18 additional DNA sequence variations in the gene encoding apolipoprotein E to explaining variation in quantitative measures of lipid metabolism

Apolipoprotein E (ApoE) is a major constituent of many lipoprotein particles. Previous genetic studies have focused on six genotypes defined by three alleles, denoted epsilon2, epsilon3, and epsilon4, encoded by two variable exonic sites that segregate in most populations. We have reported studies of the distribution of alleles of 20 biallelic variable sites in the gene encoding the ApoE molecule within and among samples, ascertained without regard to health, from each of three populations: African Americans from Jackson, Miss.; Europeans from North Karelia, Finland; and non-Hispanic European Americans from Rochester, Minn. Here we ask (1) how much variation in blood levels of ApoE (lnApoE), of total cholesterol (TC), of high-density lipoprotein cholesterol (HDL-C), and of triglyceride (lnTG) is statistically explained by variation among APOE genotypes defined by the epsilon2, epsilon3, and epsilon4 alleles; (2) how much additional variation in these traits is explained by genotypes defined by combining the two variable sites that define these three alleles with one or more additional variable sites; and (3) what are the locations and relative allele frequencies of the sites that define multisite genotypes that significantly improve the statistical explanation of variation beyond that provided by the genotypes defined by the epsilon2, epsilon3, and epsilon4 alleles, separately for each of the six gender-population strata. This study establishes that the use of only genotypes defined by the epsilon2, epsilon3, and epsilon4 alleles gives an incomplete picture of the contribution that the variation in the APOE gene makes to the statistical explanation of interindividual variation in blood measurements of lipid metabolism. The addition of variable sites to the genotype definition significantly improved the ability to explain variation in lnApoE and in TC and resulted in the explanation of variation in HDL-C and in lnTG. The combination of additional sites that explained the greatest amount of trait variation was different for different traits and varied among the six gender-population strata. The role that noncoding variable sites play in the explanation of pleiotropic effects on different measures of lipid metabolism reveals that both regulatory and structural functional variation in the APOE gene influences measures of lipid metabolism. This study demonstrates that resequencing of the complete gene in a sample of >/=20 individuals and an evaluation of all combinations of the identified variable sites, separately for each population and interacting environmental context, may be necessary to fully characterize the impact that a gene has on variation in related traits of a metabolic system.

An interaction between apo C-III variants and protease inhibitors contributes to high triglyceride/low HDL levels in treated HIV patients

BACKGROUND

Long-term therapy with protease inhibitors (PI) is associated with hypertriglyceridaemia, low high-density lipoprotein (HDL) levels and accumulation of apolipoprotein (apo) E- and apo C-III-containing lipoproteins.

OBJECTIVES

To evaluate the impact, on this dyslipaemic phenotype, of three polymorphisms of the apo C-III gene: two on an insulin response element and one in the 3'-region. Apo E genotypes were evaluated also.

DESIGN

Sixty consecutive male patients attending the HIV follow-up consultation were included during a 3-month period. All patients received at least one PI. Apo C-III and apo E genotypes were determined. Besides routine bio-clinical examination, a detailed exploration of lipoproteins and of insulin secretion markers was carried out.

METHODS

Plasma lipoparticles, insulin, proinsulin and C-peptide were measured by specific immuno-assays. Determination of apo C-III genotypes (-455C/T, -482C/T and SstI) and of apo E alleles (epsilon2, epsilon3 and epsilon4) were performed by amplification and endonuclease digestion and were confirmed by allele-specific oligonucleotide hybridization.

RESULTS

Distribution of apo C-III alleles defined four major haplotypes. Carriers of the -455C variant had 30% lower levels of HDL-cholesterol than non-carriers. Plasma triglycerides increased according to the number of variant alleles. In multivariate analysis, a model including age, body mass index, clinical stage and treatment length, plasma insulin and apo C-III haplotypes explained around 43% of the HDL-cholesterol and triglycerides variability. Measurements of lipids before and after the use of PI demonstrated synergistic effects of the treatment and apo C-III variants on triglyceride levels.

CONCLUSIONS

Apo C-III polymorphisms might identify a genetic predisposition to develop dyslipidaemia under PI therapy.

Definition of the phenotype

Definition of the phenotype is a key issue in designing any genetic study whose goal is to detect disease genes. This chapter describes strategies to increase the power to detect susceptibility loci for complex diseases. A narrowly defined disease phenotype can offer advantages over broad definitions. Studies of clinical disease can also benefit from judicious selection of endophenotypes and related quantitative traits for analysis. The effect of diagnostic and measurement error is also discussed; power is maximized when strategies to reduce error are incorporated into a study design.

Apolipoprotein E variation at the sequence haplotype level: implications for the origin and maintenance of a major human polymorphism

Three common protein isoforms of apolipoprotein E (apoE), encoded by the epsilon2, epsilon3, and epsilon4 alleles of the APOE gene, differ in their association with cardiovascular and Alzheimer's disease risk. To gain a better understanding of the genetic variation underlying this important polymorphism, we identified sequence haplotype variation in 5.5 kb of genomic DNA encompassing the whole of the APOE locus and adjoining flanking regions in 96 individuals from four populations: blacks from Jackson, MS (n=48 chromosomes), Mayans from Campeche, Mexico (n=48), Finns from North Karelia, Finland (n=48), and non-Hispanic whites from Rochester, MN (n=48). In the region sequenced, 23 sites varied (21 single nucleotide polymorphisms, or SNPs, 1 diallelic indel, and 1 multiallelic indel). The 22 diallelic sites defined 31 distinct haplotypes in the sample. The estimate of nucleotide diversity (site-specific heterozygosity) for the locus was 0.0005+/-0.0003. Sequence analysis of the chimpanzee APOE gene showed that it was most closely related to human epsilon4-type haplotypes, differing from the human consensus sequence at 67 synonymous (54 substitutions and 13 indels) and 9 nonsynonymous fixed positions. The evolutionary history of allelic divergence within humans was inferred from the pattern of haplotype relationships. This analysis suggests that haplotypes defining the epsilon3 and epsilon2 alleles are derived from the ancestral epsilon4s and that the epsilon3 group of haplotypes have increased in frequency, relative to epsilon4s, in the past 200,000 years. Substantial heterogeneity exists within all three classes of sequence haplotypes, and there are important interpopulation differences in the sequence variation underlying the protein isoforms that may be relevant to interpreting conflicting reports of phenotypic associations with variation in the common protein isoforms.

Common apolipoprotein A-IV variants are associated with differences in body mass index levels and percentage body fat

OBJECTIVE

To determine the relationship between two common apoA-IV variants (Thr347-->Ser; Gln360-->His), and body mass index (BMI) and percentage body fat.

DESIGN

Cross-sectional study.

SUBJECTS

Eight-hundred and forty-eight subjects screened for participation in ongoing clinical studies.

MEASUREMENTS

ApoA-IV genotype, body mass index, waist-to-hip ratio and percentage body fat by bioelectric impedance.

RESULTS

Participants had an average age of 41+/-12 y and an average BMI of 28.2+/-5.5 kg/m2. Individuals homozygous for the Ser347 allele had higher BMI (32.3+/-6.6 vs 28.6+/-5.3 kg/m2; P<0.01) and percentage body fat (36.9+/-7.8 vs 31.0+/-9.6%; P<0.05) compared with individuals homozygous for Thr347. In contrast, the presence of at least one copy of the His360 allele was associated with lower BMI (27.2+/-5.0 vs 28.4+/-5.6 kg/m2; P<0.05) and percentage body fat (28.6+/-8.2 vs 30.7+/-9.1%; P<0.05). The genotype effects persisted after normalization of the data for the potential confounding effects of gender, age and race. When grouped by BMI percentile, the frequency of the Ser347/Ser347 genotype increased while the frequency of the His360 allele decreased with increasing BMI.

CONCLUSIONS

These data suggest a role for apoA-IV in fat storage or mobilization and that genetic variations in the apoA-IV gene may play a role in the development of obesity.

Genetic association of five apolipoprotein polymorphisms with serum lipoprotein-lipid levels in African blacks

Genetic studies carried out mainly in European and European-derived populations have shown that common polymorphisms in genes coding for apolipoproteins are significant determinants of serum lipoprotein-lipid levels variation. However, except for a few sporadic studies, the distribution of apolipoprotein polymorphisms and their association with serum lipoprotein-lipid levels have not been evaluated systematically in African or African-derived populations. In this investigation we have studied five apolipoprotein polymorphisms, including APOA1/MspI-75 bp, APOA1/MspI+83 bp, APOC3/PvuII, APOE, and APOH in 786 Africans (493 men, 293 women) from Nigeria. The sample is comprised of Nigerian civil servants consisting of 462 junior staff (less affluent) and 324 senior staff (more affluent) where staff status is a correlate of their socioeconomic status. We first examined genetic associations in the total sample stratified by gender to determine the role of apolipoprotein polymorphisms in affecting serum lipid profile in the general population, and then by staff status to evaluate possible gene-environment interactions. In the total sample, the APOC3/PvuII polymorphism showed significant effect on HDL-cholesterol (P = 0.029) and HDL3-cholesterol (P = 0.009) in women, and the APOE polymorphism was significantly associated with total cholesterol (P = 0.031) and LDL-cholesterol (P = 0.0006) in women. Multiple regression analyses showed that the APOC3/PvuII polymorphism accounts for about 2 and 3% of the variation in HDL-cholesterol and HDL3-cholesterol, respectively, in women; while the APOE polymorphism accounted for about 5 and 6% of the variation in total- and LDL-cholesterol, respectively, in women. Whereas the association of the APOE polymorphism was independent of the staff status, the significant affect of the APOC3/PvuII polymorphism on HDL- and HDL3-cholesterol was confined to senior staff women where it explained about 7% of their variation. We also observed an interaction between staff and the APOH polymorphism in affecting cholesterol levels. The APOH polymorphism showed significant association with total cholesterol (P = 0.010) and LDL-cholesterol (P = 0.016) in senior staff women and explained about 7 and 5% of their phenotypic variations, respectively. These data indicate that gene-environment interaction may play an important role in affecting serum lipid profile in African populations.

Evidence of linkage of familial hypoalphalipoproteinemia to a novel locus on chromosome 11q23

Coronary heart disease (CHD) accounts for half of the 1 million deaths annually ascribed to cardiovascular disease and for almost all of the 1.5 million acute myocardial infarctions. Within families affected by early and apparently heritable CHD, dyslipidemias have a much higher prevalence than in the general population; 20%-30% of early familial CHD has been ascribed to primary hypoalphalipoproteinemia (low HDL-C). This study assesses the evidence for linkage of low HDL-C to chromosomal region 11q23 in 105 large Utah pedigrees ascertained with closely related clusters of early CHD and expanded on the basis of dyslipidemia. Linkage analysis was performed by use of 22 STRP markers in a 55-cM region of chromosome 11. Two-point analysis based on a general, dominant-phenotype model yielded LODs of 2.9 for full pedigrees and 3.5 for 167 four-generation split pedigrees. To define a localization region, model optimization was performed using the heterogeneity, multipoint LOD score (mpHLOD). This linkage defines a region on 11q23.3 that is approximately 10 cM distal to-and apparently distinct from-the ApoAI/CIII/AIV gene cluster and thus represents a putative novel localization for the low HDL-C phenotype.

The effect of a gender difference in the apolipoprotein E gene DNA polymorphism on serum lipid levels in a Serbian healthy population

To date, no data have been available on relationship between apolipoprotein E polymorphism and lipid levels in Serbian populations. Blood samples were obtained from 591 healthy normal individuals (193 women and 398 men). A 244 bp sequence of the apolipoprotein E gene including the two polymorphic sites was amplified by polymerase chain reaction. After digestion with Hhal, DNA fragments were visualized by microplate array diagonal gel electrophoresis. In men, levels of both total and low-density lipoprotein cholesterol among the three apolipoprotein E genotype groups differed significantly (p <0.05). The epsilon2 allele was associated with lower concentrations of both total and low-density lipoprotein cholesterol, where the epsilon4 allele had the opposite effects. No significant effects of apolipoprotein E polymorphism on serum lipid levels were observed in women. The presented data could be taken into consideration in any future disease risk evaluation in this population.

Apolipoprotein E genotype: epsilon32 women are protected while epsilon43 and epsilon44 men are susceptible to ischemic heart disease: the Copenhagen City Heart Study

OBJECTIVES

We tested the hypothesis that risk of ischemic heart disease (IHD) differs as a function of apolipoprotein E (APOE) genotype in women and men.

BACKGROUND

Apolipoprotein E genotype influences lipids and lipoproteins and, therefore, possibly the risk of IHD.

METHODS

We genotyped 9,241 white women and men from the general population and 940 white women and men with IHD.

RESULTS

Test of interaction suggested that APOE genotype may influence risk of IHD differently in women and men (p = 0.07). After age adjustment, the odds ratio (OR) for IHD for epsilon32 versus epsilon33 women was 0.57 (95% confidence interval [CI]: 0.35 to 0.94) while epsilon43 and epsilon44 versus epsilon33 men had ORs of 1.16 (0.96 to 1.41) and 1.58 (1.01 to 2.45). After adjustment for age and other conventional cardiovascular risk factors, the equivalent ORs were for epsilon32 women 0.38 (0.18 to 0.79), for epsilon43 men 1.35 (1.02-1.78) and for epsilon44 men 1.58 (0.80 to 3.08). Equivalent ORs for epsilon43 and epsilon44 versus epsilon33 women and for epsilon32 versus epsilon33 men were all close to 1.0 and nonsignificant. Of the total risk of IHD relative to the epsilon33 genotype, the fraction attributed to epsilon32 in women was -9%, while the fractions attributed to epsilon43 and epsilon44 in men were +8% and +2%.

CONCLUSIONS

Relative to epsilon33 individuals, epsilon32 women are protected while epsilon43 and epsilon44 men are particularly susceptible to IHD.

Relevance of apolipoprotein E polymorphism for coronary artery disease in the Saudi population

BACKGROUND

The apolipoprotein E alleles epsilon2 and epsilon4 have been reported as independent risk factors for coronary artery disease (CAD) and as predictors for the development of atherosclerosis.

METHODS AND RESULTS

We determined by polymerase chain reaction the distribution of apolipoprotein E polymorphism in 320 Saudi blood donors (BD), 96 CAD patients, and 40 control subjects who had undergone angiography. Compared to controls, only epsilon4 was elevated in CAD patients. More than 61% (P <.0001) of the patients had angina, and 52.1% (P <.05) were diabetic; both of these factors were strongly associated with the presence of allele epsilon2. The epsilon2 allele was also associated with hypertension, elevated serum triglycerides, and total cholesterol. On the other hand, the allele epsilon4 appeared to be associated with increased risk of CAD and was also associated with hypertension, 3-vessel disease, and restenosis.

CONCLUSIONS

Accordingly, epsilon4 may be associated with increased risk of CAD, whereas epsilon2 appears to be a predictor of several risk factors for atherosclerosis.

Utility of the predictors of coronary heart disease mortality in a longitudinal study of elderly Finnish men aged 65 to 84 years is dependent on context defined by Apo E genotype and area of residence

A common assumption underlying most genetic studies is that individuals with different genotypes respond similarly to exposure to internal (epigenetic and background genotype effects) and external (ecological) environments. Here we evaluate whether this assumption is true in individuals with different genotypes of the gene coding for the apolipoprotein E (Apo E) molecule, an important determinant of the metabolic fate of plasma lipids and lipoproteins. We addressed whether the utility of known risk factors of coronary heart disease (CHD) in the prediction of CHD death in a 5-year follow-up is the same for the two most common Apo E genotypes, epsilon3/3 and epsilon4/3, in two cohorts of elderly Finnish men (age at baseline: 65-84 years), one in Eastern and the other in Southwestern Finland. The CHD mortality rate was higher in the epsilon4/3 than in the epsilon3/3 genotype in both cohorts (11.1 versus 7.8%, Pr = 0.281 in the Eastern cohort and 19.6 versus 8.2%, Pr = 0.002 in the Southwestern cohort). In the Eastern cohort, serum high density lipoprotein (HDL) cholesterol level was identified as a strong predictor of CHD death in the epsilon3/3 genotype (beta = -2.155, Pr = 0.019). In the Southwestern cohort, age (beta = 0.139, Pr = 0.006), body mass index (BMI) (beta = 0.149, Pr = 0.016), and serum total cholesterol level (beta = 0.453, Pr = 0.051) were identified as strong predictors in the epsilon3/3 genotype, as were smoking (beta = 0.236, Pr = 0.008) and BMI (beta = -0.124, Pr = 0.057) in the epsilon4/3 genotype. The latter observation indicates that in Southwestern Finland the probability of CHD death decreases with increasing BMI in elderly men with the epsilon4/3 genotype, while in their counterparts with the epsilon3/3 genotype the risk increases with increasing BMI. This difference was statistically significant (Pr = 0.002). These observations clearly argue against the assumption that individuals with different genotypes respond similarly to exposures to internal and/or external environments. These observations are consistent with a complex pathobiology of CHD involving biochemical and physiological agents that are under the influence of interactions between genetic and environmental factors. Information about these interactions is necessary for developing a more precise risk assessment and ultimately to improve public health and clinical strategies to prevent this devastating disease both at the individual and population levels.

Apolipoprotein E polymorphism in men and women from a Spanish population: allele frequencies and influence on plasma lipids and apolipoproteins

The apolipoprotein (apo) E phenotype and its influence on plasma lipid and apolipoprotein levels were determined in men and women from a working population of Madrid, Spain. The relative frequencies of alleles epsilon(2), epsilon(3) and epsilon(4) for the study population (n=614) were 0.080, 0.842 and 0.078, respectively. In men, apo E polymorphism was associated with variations in plasma triglyceride and very low-density lipoprotein (VLDL) lipid levels. It was associated with the proportion of apo C-II in VLDL, and explained 5.5% of the variability in the latter parameter. In women apo E polymorphism was associated with the concentrations of plasma cholesterol and low-density lipoprotein (LDL) and high-density lipoprotein (HDL) related variables. The allelic effects were examined taking allele epsilon(3) homozygosity as reference. In men, allele epsilon(2) significantly increased VLDL triglyceride and VLDL cholesterol concentrations, and this was accompanied by an increase of the apo C-II content in these particles. Allele epsilon(4) did not show any significant influence on men's lipoproteins. In women, allele epsilon(2) lowered LDL cholesterol and apo B levels, while allele epsilon(4) increased LDL cholesterol and decreased the concentrations of HDL cholesterol, HDL phospholipid and apo A-I. These effects were essentially maintained after excluding postmenopausal women and oral contraceptive users from the analysis.

IN CONCLUSION

(1) the population of Madrid, similar to other Mediterranean populations, exhibits an underexpression of apo E4 compared to the average prevalence in Caucasians, (2) gender interacts with the effects of apo E polymorphism: in women, it influenced LDL and HDL levels, whereas in men it preferentially affected VLDL, and (3) allele epsilon(2) decreased LDL levels in women, while it increased both VLDL lipid levels and apo C-II content in men, but, in contrast to allele epsilon(4), it did not show an impact on HDL in either sex.

Apolipoprotein A-IV-2 allele: association of its worldwide distribution with adult persistence of lactase and speculation on its function and origin

Apolipoprotein A-IV (apo A-IV) is a 46-Kd plasma glycoprotein that may play a major role in intestinal lipid absorption. A genetic polymorphism in the apo A-IV gene, apo A-IV-2, encodes a His-->Gln substitution at codon 360 that alters the biological function of this apolipoprotein. As the worldwide distribution of the apo A-IV-2 allele appeared similar to the frequency of a genetic polymorphism that determines the persistence of lactase into adulthood, we examined the relationship between the apo A-IV-2 and lactase persistence polymorphisms by compiling the prevalence of adult lactase persistence in all populations in which the frequency of the apo A-IV-2 allele has been determined. Across 29 groups, there was an extremely strong correlation (4 = 0.937, P < 0.000001) between apo A-IV-2 allele frequency and the prevalence of adult lactase persistence. Apo A-IV-2 allele frequency was highest in Iceland, an ancient Viking colony, and decreased across Europe in a north-to-south and west-to-east gradient, generally following hypothetical isoclines for the lactase persistence gene. There were no correlations between the population frequencies of the apo E2, E3, or E4 alleles and either the prevalence of lactase persistence or the frequency of the apo A-IV-2 allele. In light of the effects of the apo A-IV-2 polymorphism on lipid metabolism, we speculate that the apo A-IV-2 allele may have originated in ancient Scandinavia, spread by conferring a nutritional advantage in the setting of a lifelong high milkfat intake, and was later carried southwards by the Viking incursions into Europe.

The genetics of serum lipid responsiveness to dietary interventions

CHD is a multifactorial disease that is associated with non-modifiable risk factors, such as age, gender and genetic background, and with modifiable risk factors, including elevated total cholesterol and LDL-cholesterol levels. Lifestyle modification should be the primary treatment for lowering cholesterol values. The modifications recommended include dietary changes, regular aerobic exercise, and normalization of body weight. The recommended dietary changes include restriction in the amount of total fat, saturated fat and cholesterol together with an increase in the consumption of complex carbohydrate and dietary fibre, especially water-soluble fibre. However, nutrition scientists continue to question the value of these universal concepts and the public health benefits of low-fat diets, and an intense debate has been conducted in the literature on whether to focus on reduction of total fat or to aim efforts primarily towards reducing the consumption of saturated and trans fats. Moreover, it is well known that there is a striking variability between subjects in the response of serum cholesterol to diet. Multiple studies have examined the gene-diet interactions in the response of plasma lipid concentrations to changes in dietary fat and/or cholesterol. These studies have focused on candidate genes known to play key roles in lipoprotein metabolism. Among the gene loci examined, APOE has been the most studied, and the current evidence suggests that this locus might be responsible for some of the inter-individual variability in dietary response. Other loci, including APOA4, APOA1, APOB, APOC3, LPL and CETP have also been found to account for some of the variability in the fasting and fed states.

Coronary heart disease. At the interface of molecular genetics and preventive medicine

BACKGROUND

Susceptibility to common chronic diseases such as coronary heart disease (CHD) appears to be influenced by "context-dependent effects," which include interactions among genes (genetic epistasis) and among genes and environmental factors (gene-environment interactions).

METHODS

A synthesis of current knowledge and research findings demonstrates the importance of integrating genetic research on cardiovascular disease with preventive medicine and public health initiatives.

RESULTS

A variety of candidate genes have been implicated in risk for CHD, but only limited examples of context-dependent effects have been described. Interactions between genetic and environmental factors appear to influence lipid metabolism, plasma homocysteine levels, and pharmacologic response to many commonly prescribed medications. Quantification of genetic effects associated with increased disease risk that are modifiable by interventions such as diet, exercise, and smoking cessation is an important interface between molecular genetics and preventive medicine.

CONCLUSIONS

As a primary focus of preventive medicine expands to encompass early detection and treatment of asymptomatic individuals at risk for disease, the ability to quantify the influence of context-dependent effects on disease risk will be critical for determining drug safety and effectiveness in diverse patient populations and for implementing effective prevention and treatment programs.

Association of apolipoprotein E polymorphism and concentration with serum lipids and apolipoprotein level in the Chinese from Shanghai

The influence of apolipoprotein E polymorphism and apoE level on serum lipids and apolipoproteins was investigated in 71 healthy people and 43 patients with coronary artery disease from Shanghai. The frequency of apoE alleles was 0.06 for epsilon2, 0.86 for epsilon3, and 0.07 for epsilon4 in the healthy group, and 0.14 for epsilon2, 0.77 for epsilon3, and 0.09 for epsilon4 in the coronary artery disease group. There was no significant difference in the frequency of apoE alleles between these two groups. Serum levels of triglyceride and apo AI did not differ according to apoE genotypes, whereas serum level of apoB was significantly different according to apoE genotypes (p<0.05) both in healthy and coronary artery disease groups. However, in the healthy group, apo epsilon2 allele carriers had significantly higher level of apoE than apo epsilon3 and epsilon4 allele carriers (p<0.001) and apo epsilon4 allele carriers had significantly higher level of total cholesterol than apo epsilon3 and epsilon2 allele carriers. These were not observed in the coronary artery disease group. ApoE concentration was positively correlated with cholesterol, apoAI, and apoB levels in the control subjects and no significant correlation was observed with triglyceride level. In contrast, apoE level was positively related only to triglyceride level in the coronary artery disease group. In the control group, apoE genotypes and apoE level explained together 19.3% and 26.6% of the variability of apoB and cholesterol level, respectively, apoE polymorphism explained 23% of the variability of apoE level and apoE level explained 13.2% of the variability of apoAI level. In the coronary artery disease group, only apoE level explained 41.7% of triglyceride variability. Finally we compared our results with those previously obtained in a French healthy population, the Stanislas cohort. Results suggested that there were some difference between the Chinese control and the French subjects.

Serum lipids and apolipoprotein E phenotypes in identical twins reared apart

Lipid and lipoprotein metabolism is controlled by genes, the environment and the gene environment interaction. We studied monozygotic twin pairs reared apart (MZA) and an age sex matched group of twins reared together (MZT) to evaluate the effects of the genotype and the rearing environment on lipids. The intraclass correlations for low density lipoprotein (LDL) cholesterol were 0.21 and 0.50 for the MZA and MZT groups, respectively, suggesting that the rearing environment possibly had an impact on the variability in LDL cholesterol later in life. The intraclass correlations for total cholesterol (0.26 and 0.47 for the MZA and MZT groups, respectively) reflected those for LDL cholesterol. The intraclass correlations for high density lipoprotein (HDL) cholesterol did not show any difference between the twin groups, suggesting that the rearing environment does not have major long-term effects on the variability of HDL levels. The intrapair differences for LDL cholesterol were smallest in the twins heterozygous for the apolipoprotein E allele epsilon2 (E2/3 and E2/4 phenotypes), intermediate in the pairs with the common E3/3 phenotype and enhanced in the pairs with E4/3 phenotype. To conclude, these data suggest that the rearing environment may play a role in the variability of LDL cholesterol levels, although variance difference between MZAs and MZTs, and the small number of available monozygotic twins reared apart limits the generalizability of the results.

Lipid profiles reflecting high and low risk for coronary heart disease: contribution of apolipoprotein E polymorphism and lifestyle

To elucidate the role of modifiable factors and the apolipoprotein E polymorphism in explaining lipid profiles reflecting low, average and high risk for coronary heart disease, we selected subjects from a large population-based study. Subjects with low total cholesterol (TC) (< 15th percentile) and high HDL-cholesterol levels (> 85th percentile) were randomly selected (n = 99) and represent subjects with a low risk lipid profile. Additionally, 95 subjects with total and HDL-cholesterol levels in the 15% around the population-median (median risk lipid profile) and 100 subjects with high TC (> 85th percentile) and low HDL-cholesterol levels (< 15th percentile) (high risk lipid profile) were selected. Compared with E3/3 subjects, the likelihood for a low risk lipid profile was considerably higher (odds ratio 14.3; 2.6-79) in female, but not in male E2-carriers (1.5; 0.3-6.7). Smoking and alcohol consumption were independently associated with a low risk lipid profile in both genders, physical inactivity only in women. The odds ratio for a high risk lipid profile was elevated in male E4-carriers (4.9; 1.1-23) only. In addition to the E4 isoform, smoking and physical inactivity, overweight was the main determinant for a high risk lipid profile (odds ratio 16.8; 3.4-82). Male overweight E4-carriers had a 50 times higher likelihood of a high risk lipid profile than E3/3 men of normal weight. In women, only overweight was independently associated with a high risk lipid profile. Our results suggest that both modifiable factors and the apolipoprotein E polymorphism contribute to a lipid profile, reflecting low, average and high risk for coronary heart disease, but effects may be gender-specific.

Influence of APOH protein polymorphism on apoH levels in normal and diabetic subjects

Apolipoprotein (apo)H (also known as beta 2 glycoprotein-I) is a glycoprotein synthesized by liver cells and it is present in the blood associated with plasma lipoproteins. APOH displays a genetically determined structural polymorphism: three alleles (APOH*1, APOH*2, APOH*3) at a single locus on chromosome 17 code for different isoforms, and population studies have shown that APOH*2 is the most frequent allele. This paper assesses the relation between APOH phenotypes and plasma apoH levels in a population composed of 278 healthy subjects (243 H2/2, 32 H3/2, 2 H3/3, 1 H2/1; allele frequencies APOH*1 0.002, APOH*2 0.934, APOH*3 0.064) and 245 diabetics (212 H2/2, 30 H3/2, 3 H3/3; allele frequencies APOH*2 0.927 and APOH*3 0.073). Determination of apoH levels by competitive ELISA gave a mean value of 26.3 +/- 9.8 mg/dl for all subjects, 22.6 +/- 7.7 in normals vs 30.6 +/- 10.3 in diabetics (p = 0.0001), and 23.0 +/- 7.9, 19.3 +/- 5.4 and 18.5 +/- 3.5 mg/dl for H2/2, H3/2 and H3/3 in normals and 31.1 +/- 10.1, 28.2 +/- 10.8 and 15.7 +/- 9.0 mg/dl in diabetics, respectively. ANCOVA of the adjusted data revealed a significant difference in apoH levels for the three phenotypes in both the normal subjects (p = 0.01) and the diabetics (p = 0.02). ANCOVA of the whole samples of subjects, controlling for diabetes as well as age, sex and total cholesterol, indicated a substantial effect of phenotype, independent of the other variables (p = 0.0007).

Preliminary report of a genetic basis for cognitive decline after cardiac operations. The Neurologic Outcome Research Group of the Duke Heart Center

BACKGROUND

Changes in memory and cognition frequently follow cardiac operations. We hypothesized that patients with the apolipoprotein E-epsilon 4 allele are genetically predisposed to cognitive dysfunction after cardiac operations.

METHODS

The apolipoprotein E-epsilon 4 allele was evaluated as a predictor variable for postoperative cognitive dysfunction in 65 patients undergoing cardiac bypass grafting at Duke University Medical Center. The primary outcome measure was performance on a cognitive battery administered preoperatively and at 6 weeks postoperatively.

RESULTS

In a multivariable logistic regression analysis including apolipoprotein E-epsilon 4, preoperative score, age, and years of education, a significant association was found between apolipoprotein E-epsilon 4 and change in cognitive test score in measures of short-term memory at 6 weeks postoperatively. Patients with lower educational levels were more likely to show a decline in cognitive function associated with the apolipoprotein E-epsilon 4 allele.

CONCLUSIONS

This study suggests that apolipoprotein E genotype is related to cognitive dysfunction after cardiopulmonary bypass. Cardiac surgical patients may be susceptible to deterioration after physiologic stress as a result of impaired genetically determined neuronal mechanisms of maintenance and repair.

A dietary and behavioral intervention designed to lower coronary heart disease. Risk factors are unaffected by variation at the APOE gene locus

Variation at the apolipoprotein E (APOE) gene locus has demonstrated a consistent impact on lipoprotein levels. APOE typing was performed for 488 healthy, caucasian, premenopausal women participating in the Women's Healthy Lifestyle Project (WHLP) aimed at reducing total fat, saturated fat and cholesterol intake and promoting physical activity. Women in both the intervention and control groups were included in the trial. The purpose of the present study was to determine whether the magnitude of the changes in total cholesterol (Tc), low density lipoprotein cholesterol (LDLc) and high density lipoprotein cholesterol (HDLc) due to the dietary intervention were dependent on the variation in APOE. Weight, body mass index (BMI), and lipoprotein levels were measured at baseline and at a 6 month follow-up. ANOVA was used to determine whether the change in Tc and LDLc was dependent on dietary intervention and variation at APOE levels. The levels of Tc and LDLc were higher in women with the APOE*4 genotype. There were no statistically significant effects of APOE genotype and changes in Tc and LDLc (P > 0.1). Adjusted Tc and LDLc changes were comparable in the 3 APOE subgroups (Tc = -14.3, -12.9 and -11.7 mg/dl; LDLc = -12.1, -10.7 and -10.7 mg/dl, respectively as above). In conclusion, the genetic (APOE) background of premenopausal women in this study did not have a significant effect on their response to dietary intervention.