Apolipoprotein genetic variation in the assessment of atherosclerosis susceptibility

Clinical review on triglycerides

Hypertriglyceridaemia is a common clinical problem. Epidemiologic and genetic studies have established that triglyceride-rich lipoproteins (TRL) and their remnants as important contributors to ASCVD while severe hypertriglyceridaemia raises risk of pancreatitis. While low-density lipoprotein is the primary treatment target for lipid lowering therapy, secondary targets that reflect the contribution of TRL such as apoB and non-HDL-C are recommended in the current guidelines. Reduction of severely elevated triglycerides is important to avert or reduce the risk of pancreatitis. Here we discuss interventions for hypertriglyceridaemia, including diet and lifestyle, established treatments such as fibrates and omega-3 fatty acid preparations and emerging therapies, including various biological agents.

2019 George Lyman Duff Memorial Lecture: Three Decades of Examining DNA in Patients With Dyslipidemia

Dyslipidemias include both rare single gene disorders and common conditions that have a complex underlying basis. In London, ON, there is fortuitous close physical proximity between the Lipid Genetics Clinic and the London Regional Genomics Centre. For >30 years, we have applied DNA sequencing of clinical samples to help answer scientific questions. More than 2000 patients referred with dyslipidemias have participated in an ongoing translational research program. In 2013, we transitioned to next-generation sequencing; our targeted panel is designed to concurrently assess both monogenic and polygenic contributions to dyslipidemias. Patient DNA is screened for rare variants underlying 25 mendelian dyslipidemias, including familial hypercholesterolemia, hepatic lipase deficiency, abetalipoproteinemia, and familial chylomicronemia syndrome. Furthermore, polygenic scores for LDL (low-density lipoprotein) and HDL (high-density lipoprotein) cholesterol, and triglycerides are calculated for each patient. We thus simultaneously document both rare and common genetic variants, allowing for a broad view of genetic predisposition for both individual patients and cohorts. For instance, among patients referred with severe hypertriglyceridemia, defined as ≥10 mmol/L (≥885 mg/dL), <1% have a mendelian disorder (ie, autosomal recessive familial chylomicronemia syndrome), ≈15% have heterozygous rare variants (a >3-fold increase over normolipidemic individuals), and ≈35% have an extreme polygenic score (a >3-fold increase over normolipidemic individuals). Other dyslipidemias show a different mix of genetic determinants. Genetic results are discussed with patients and can support clinical decision-making. Integrating DNA testing into clinical care allows for a bidirectional flow of information, which facilitates scientific discoveries and clinical translation.

Genetics of Hypertriglyceridemia

Hypertriglyceridemia, a commonly encountered phenotype in cardiovascular and metabolic clinics, is surprisingly complex. A range of genetic variants, from single-nucleotide variants to large-scale copy number variants, can lead to either the severe or mild-to-moderate forms of the disease. At the genetic level, severely elevated triglyceride levels resulting from familial chylomicronemia syndrome (FCS) are caused by homozygous or biallelic loss-of-function variants in LPL, APOC2, APOA5, LMF1, and GPIHBP1 genes. In contrast, susceptibility to multifactorial chylomicronemia (MCM), which has an estimated prevalence of ~1 in 600 and is at least 50-100-times more common than FCS, results from two different types of genetic variants: (1) rare heterozygous variants (minor allele frequency <1%) with variable penetrance in the five causal genes for FCS; and (2) common variants (minor allele frequency >5%) whose individually small phenotypic effects are quantified using a polygenic score. There is indirect evidence of similar complex genetic predisposition in other clinical phenotypes that have a component of hypertriglyceridemia, such as combined hyperlipidemia and dysbetalipoproteinemia. Future considerations include: (1) evaluation of whether the specific type of genetic predisposition to hypertriglyceridemia affects medical decisions or long-term outcomes; and (2) searching for other genetic contributors, including the role of genome-wide polygenic scores, novel genes, non-linear gene-gene or gene-environment interactions, and non-genomic mechanisms including epigenetics and mitochondrial DNA.

Lipid-Lowering Agents

Several new or emerging drugs for dyslipidemia owe their existence, in part, to human genetic evidence, such as observations in families with rare genetic disorders or in Mendelian randomization studies. Much effort has been directed to agents that reduce LDL (low-density lipoprotein) cholesterol, triglyceride, and Lp[a] (lipoprotein[a]), with some sustained programs on agents to raise HDL (high-density lipoprotein) cholesterol. Lomitapide, mipomersen, AAV8.TBG.hLDLR, inclisiran, bempedoic acid, and gemcabene primarily target LDL cholesterol. Alipogene tiparvovec, pradigastat, and volanesorsen primarily target elevated triglycerides, whereas evinacumab and IONIS-ANGPTL3-L_Rx target both LDL cholesterol and triglyceride. IONIS-APO(a)-L_Rx targets Lp(a).

Epidemiology of Cerebrovascular Disease Among Chinese Canadian Adults With Type 2 Diabetes

BACKGROUND

First-generation Chinese Canadians have usually maintained different lifestyles before immigration to North America, and the question of whether Chinese Canadians with type 2 diabetes have a different stroke profile than that of non-Chinese Canadians remains unanswered.

OBJECTIVES

To determine whether 1) Chinese Canadians who have had a stroke within the last 15 years are more likely to have diabetes than non-Chinese Canadians and 2) to explore differences in stroke profiles between the 2 cohorts.

METHODS

Age- and sex-matched Chinese Canadians (n=70) and non-Chinese Canadians (n=107) were compared on the basis of stroke type, age at stroke onset, stroke etiology and common risk factors. Classifications for disease were done according to professional guidelines. Statistical analysis was done with Student t test and odds ratios to confirm differences between groups.

RESULTS

Chinese Canadians with stroke had a higher frequency of diabetes mellitus than non-Chinese Canadians. Chinese Canadians with diabetes were more likely to have small vessel disease, specifically lacunar stroke. Chinese Canadians at high risk for stroke were more likely to have a poor prognosis than non-Chinese Canadians, with near significance.

CONCLUSION

Chinese Canadians with diabetes who had ischemic strokes were especially susceptible to intracranial small vessel disease compared with non-Chinese Canadians. These results signify that risk factor prevalence and stroke types differ considerably between Chinese Canadians and non-Chinese Canadians residing in Toronto, warranting further study.

Impact of genetic variation on metabolic response of bone to diet

There is compelling evidence to suggest that both the development of bone to peak bone mass at maturity and subsequent loss depend on the interaction between genetic, hormonal, environmental and nutritional factors. The major part (≤80%) of the age-specific variation in bone turnover and bone density is genetically determined. However, the notion of genetic determinant is of little value unless the specific genes that are involved can be identified. Most work in this area of osteoporosis research has focused on the candidate gene approach, which has identified several candidate genes for osteoporosis, including genes encoding the vitamin D receptor (VDR), oestrogen receptors (α and β), apolipoprotein E, collagen type I α 1 and methylenetetrahydrofolate reductase, amongst many others. However, in general, findings from numerous studies of the association between such genes and various bone variables have been inconsistent. In addition to possible gene—gene interactions it is likely that there are interactions between these genes and certain environmental factors, especially nutrition, that may mediate expression of bone-related phenotypes. While these potential interactions add a level of complexity to our understanding of these apparent genetic effects on bone, identification of a role for genetic factors without knowledge of their interaction with nutrients can do little to advance prevention and treatment of osteoporosis. This information is especially important because, unlike genotype, diet and nutrition can be modified. The aim of the present review is to critically evaluate current knowledge relating to candidate genes for osteoporosis, with particular emphasis on their interaction with nutrients and dietary factors in determining bone health.

Apolipoprotein B gene polymorphisms in patients from Serbia with ischemic cerebrovascular disease

The plasma concentration of apoB has recently been reported to be the best lipid predictor of coronary heart disease. The possible associations of genetic markers in the apolipoprotein B gene (XbaI, EcoRI, MspI, Ins/Del, and 4311 A/G polymorphisms) were evaluated in patients with ischemic cerebrovascular disease (ICVD) and controls of equivalent BMI. The odds ratio for ICVD in the X+X+ genotype was 2.22, 95% CI 1.24-3.96 (P<0.05), while that for ICVD in the Ins/Ins genotype was 2.82, 95% CI 1.57-5.06 (P<0.05). The patients had significantly higher frequency of the 4311A allele compared to the controls (P<0.01). Our results support the assumption that apoB gene polymorphisms may contribute to the extent of cerebrovascular disease risk.

An investigation of human apolipoproteins B and E polymorphisms in two African populations from Ethiopia and Benin

Three polymorphisms (XbaI, EcoRI, and Ins/Del) of the apolipoprotein B (APOB) gene and the polymorphism of apolipoprotein E (APOE) were investigated in two population samples of Amhara and Oromo origin from Ethiopia, and in two population samples of Bariba and Berba origin from Benin. No heterogeneity was observed within each major group. The cumulated frequencies of the APOB X+, R+, and D alleles for the Ethiopia and the Benin groups were 0.268 and 0.133, 0.958 and 0.818, 0.206 and 0.223, respectively. Regarding APOE, the cumulated allele frequencies of Ethiopia and Benin were 0.031 and 0.103 for epsilon*2 allele, 0.811 and 0.742 for epsilon*3, and 0.143 and 0.155 for epsilon*4, respectively. APOE typing performed at the protein level only in the Ethiopians revealed a variant allele, epsilon*5, found at the polymorphic level both in the Amhara and in the Oromo (cumulated frequency: 0.015). A tentative explanation for the higher frequencies of epsilon*4 and epsilon*5 alleles was sought in relation to the lifestyle and ethnicity of the two populations. Am. J. Hum. Biol. 11:297-304, 1999. Copyright 1999 Wiley-Liss, Inc.

Association of an apolipoprotein B gene marker with essential hypertension

We designed an association (retrospective, case control) study aimed at evaluating associations between genetic variations of the human apolipoprotein B (apoB) gene and clinical diagnosis of essential hypertension. Our approach was to compare the distribution of the alleles of a highly polymorphic variable number of tandem repeats localized 3' to the human apoB gene, the apoB 3' hypervariable region (HVR), in a group of normotensive and a group of hypertensive individuals. We collected DNA samples from 437 unrelated nationals (215 normotensives and 222 hypertensives) from the United Arab Emirates (UAEs), and we determined their apoB 3' HVR allele and genotype status with a polymerase chain reaction-based assay. In the UAE population, we found 18 alleles underlying a total of 51 genotypes. The distribution of these alleles was significantly different between normotensive and hypertensive UAE nationals. The main peak of the distributions occurred at 35 repeats among hypertensives (with a relative frequency of 25.7% versus 19.6% in normotensives) and at 37 repeats among normotensives (28.8% versus 20.3% in hypertensives). Alleles with 21, 23, 25, 49, and 55 repeats were found in hypertensives only (with a combined relative frequency of 7.6%). We conclude that variations of the apoB gene, or of a nearby gene, that may be in linkage disequilibrium with these alleles play a role in the development of essential hypertension in the UAEs.

Apolipoprotein E genotype and plasma levels in coronary artery disease. A case-control study in the Italian population

OBJECTIVES

To investigate the role of the apolipoprotein B and apolipoprotein E polymorphisms in coronary artery disease (CAD) susceptibility in the Italian population and their relation to plasma lipid and apolipoprotein levels.

METHODS

APOB (APOB Xbal, EcoRI, Ins/Del), and APOE (APOE Cfol) polymorphisms were analyzed in 150 male CAD patients and 110 matched controls. In the same subjects plasma lipid, apoB, and apoE levels were measured.

RESULTS

No differences in the distribution of the APOB polymorphisms were observed between patients and controls. Among patients the number of e*4-carriers was significantly higher than in controls. e*4-carriers were more frequent among the hypertensive patients and had a higher systolic blood pressure (p = 0.007) than the non-e*4 carriers. The APOB Xbal polymorphism was found to influence the distribution of HDL-cholesterol. Patients showed significantly lower levels of apoE (39.29 mg/L) than controls (54.32 mg/dL) and the lowest concentrations were associated to the E4/E3 and E4/E4 genotypes.

CONCLUSION

Quantitative data are consistent with the hypothesis that apoE has an anti-atherosclerotic role and suggest that the apoE quantitation could be a useful parameter for defining cardiovascular risk. e*4 allele appears to be a risk factor for CAD in the Italian population and could act by its association with low apoE levels.

Plasma levels of apolipoprotein E and genetic markers in elderly patients with Alzheimer's disease

Besides apolipoprotein E (APOE) polymorphism, whose association with Alzheimer's disease (AD) has been confirmed in most of the numerous population samples studied, other markers have been investigated. In most cases the association firstly described was not confirmed in subsequent works. Since it is important to examine these associations in as many populations as possible, we investigated APOE, APOC1, APOC2, alpha-1 antichymotrypsin (ACT) and presenilin-1 (PS-1) polymorphisms in a series of elderly patients with late-onset sporadic AD from Northern Italy and in a sex and age-matched control group. We could not confirm the significantly higher frequency of the ACT*A allele among carriers of APOE e*4 allele described elsewhere, although a similar trend was observed. The APOC2 and the PS-1 distributions were similar between patients and controls. However, we observed a significant difference in the genotype and allele frequencies of APOE and APOC1: patients had higher e*4 and C1*2 allele frequencies. This finding confirms the important role for APOE in AD occurrence. In addition, APOC1 seems to be an interesting marker because, though in strict linkage disequilibrium with APOE, it seems to play an independent role in AD risk. In contrast to previously reported data, plasma apoE concentrations were similar in patients and in controls. An interaction between APOE and APOC1 polymorphisms and apoE levels was observed in patients: subjects carrying the APOE E3/E2 or the APOC1 2-2 genotype have higher apoE concentrations than those who do not.

Apolipoproteins B and E, and angiotensin I-converting enzyme (ACE) genetic polymorphisms in Italian women with coronary artery disease (CAD) and their relationships with plasma lipid and apolipoprotein levels

The XbaI, EcoRI and the signal peptide insertion/deletion (I/D) polymorphic sites of APOB gene, the CfoI polymorphic site of apolipoprotein E gene (APOE), and the insertion/deletion polymorphism of angiotensin I-converting enzyme (ACE) gene were studied using polymerase chain reaction (PCR) in 55 postmenopausal women with coronary artery disease (CAD) and in 119 control women of equivalent age. Patients and controls were recruited from the population of Rome, considered representative of Central and Southern Italy. There were no significant differences in allele frequencies between the two groups, though APOB X-, R- and I, APOE*3, and ACE D alleles were slightly more frequent in the cases than in the controls. The patients did not differ from the controls for plasma total cholesterol (TC), HDL-cholesterol, LDL-cholesterol, and apoAI values, while they presented significantly higher levels of triglycerides and apoB, and lower apoE levels. TC, apoE, and apoB quantitative values, adjusted for age, varied significantly among APOB XbaI and APOE genotypes. APOB X-X- genotype was associated in patients with a significantly lower mean TC concentration than the other two genotypes pooled together. APOE 3-2 genotype in the controls had significantly lower TC levels with respect to the other two pooled genotypic classes and higher apoE levels compared to 3-3 and 4-3 genotypes. In the patients, 3-2 genotype had significantly lower apoB levels than the pooled 3-3 and 4-3 class. We conclude that in the Italian women the DNA polymorphisms studied in this work do not seem to be important risk factors for CAD occurrence; that apoE quantitation could be another useful parameter to identify subjects at risk of CAD; and that APOB X- and APOE*2 are the alleles that most influence the interindividual plasma lipid variation among CAD female patients.

Genetics and behavioral medicine: risk factors for cardiovascular disease

This is the second in a series of three articles addressing the intersection of interests in behavioral genetics and behavioral medicine. In this article, we use risk factors for cardiovascular disease as a prototypical trait for which behavioral genetic approaches provide powerful tools for understanding how risk factors, behavior, and health outcomes are related. The approach synthesizes a number of methods and areas of interest in an attempt to arrive at a comprehensive, whole-organism understanding of health-related risk factors and their response to behavioral interventions.

Genetic analysis of sex and generation differences in plasma lipid, lipoprotein, and apolipoprotein levels in adolescent twins and their parents

In a sample of Dutch families consisting of parents aged 35-65 years and their twin offspring aged 14-21 years, a significant difference between generations was observed in phenotypic variances and in genetic heritabilities for plasma levels of total cholesterol, triglycerides, high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol, and apolipoproteins (apo) A1, A2, B, and E. For all traits parents were more variable than their offspring. This increase in phenotypic variance was best explained by a genetic model in which individual specific environmental variance increased with increasing age. Genetic variance was the same across generations for nearly all traits except triglycerides and apoE, for which a decrease in genetic variance was observed. This model led to large intergenerational differences in genetic heritabilities. Heritabilities for children were between 65 and 87%, while heritabilities for their parents were between 10 and 50%. No evidence was found for effects of a shared family environment.

Apolipoprotein E alleles but neither apolipoprotein B nor apolipoprotein AI/CIII alleles are associated with late onset, familial Alzheimer's disease

The possibility of a genetic association between late onset, familial Alzheimer's disease and alleles at the apolipoprotein B and AI/CIII loci have been examined. In contrast to the genetic association with the apolipoprotein E locus, no evidence for genetic associations to these loci was found.

DNA polymorphisms at the locus for human cholesteryl ester transfer protein (CETP) are associated with macro- and microangiopathy in non-insulin-dependent diabetes mellitus

The effect of variation at the cholesteryl ester transfer protein (CETP) gene locus and in the apolipoprotein (apo) AI-CIII-AIV gene cluster on the susceptibility of individuals with non-insulin-dependent diabetes mellitus (NIDDM) to atherosclerotic vascular disease was studied in 136 male and 122 female patients with NIDDM. The prevalence of myocardial infarction was high (38%) in patients with the EcoNI genotype 2-2 of the CETP gene locus (= 2-2; subjects homozygous for the absence of the restriction site) compared with patients with the genotype 1-1 (= 1-1; subjects homozygous for the presence of the restriction site) (18%, p < 0.02). The prevalence of any evidence of coronary heart disease (CHD) (presence of ischaemic ECG changes or definite myocardial infarction) was high in 2-2 (73%) compared with the genotype 1-2 (= 1-2; heterozygous for the presence of the restriction site) (52%, p < 0.02) and genotype 1-1 (p = 0.06). CHD was more prevalent in men with 2-2 (70%) than in those with 1-1 (42%, p < 0.05), but in women no significant differences were found in the prevalences of CHD between the EcoNI genotypes. Neuropathy was more often present in the patients with 2-2 (31%) than in those with 1-1 (12%, p < 0.02) or 1-2 (14%, p < 0.01). Plasma total cholesterol and total- and VLDL-triglycerides were higher in women with the EcoNI genotype 1-1 than in those with the genotype 1-2. In men no significant differences in plasma lipids were found. In addition, the prevalence of cerebrovascular disease was high (21%) in the patients with the genotype 1-1 of the TaqIB polymorphism compared with the genotype 2-2 (6%, p < 0.02). None of the alleles defined by four polymorphisms in the apo AI-CIII-AIV gene region were associated with an increased risk for macroangiopathy. The PstI polymorphism had an effect on plasma triglyceride levels. At the CETP locus one pair of loci (TaqIB and EcoNI) and three pairs of loci at the apo AI-CIII-AIV gene cluster (SacI and MspI, SacI and PvuII and MspI and PvuII) showed significant allelic association. In conclusion, the variation of CETP locus modulates the risk for diabetic complications in patients with NIDDM and the effect seems to be different between men and women. In contrast, the AI-CIII-AIV gene cluster polymorphisms seem not to be related to the risk of CHD in NIDDM.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoprotein E and B polymorphisms--longevity factors assessed in nonagenarians

To test if the prevalence of genetic risk factors for coronary heart disease (CHD) is low in individuals who have reached an extremely old age, the allele frequencies of apolipoprotein E (apo E) and B (apo B) polymorphisms and plasma lipoprotein(a) levels were investigated in nonagenarians and in younger control groups. The frequency of the epsilon 4 allele of apo E was significantly lower in the nonagenarians than in the middle-aged and young adults (P < 0.05). Also, the frequency of EcoRI allele R- of apo B was low in the nonagenarians, whereas the allele frequency for the XbaI polymorphism of apo B and plasma lipoprotein(a) concentrations did not differ between the nonagenarians and the younger groups. These findings strongly suggest that the presence of these potential genetic risk factors for CHD, namely the epsilon 4 allele of apo E and the R- allele of apo B, decreases the probability of an individual reaching an extremely old age.

Pattern of cerebral atherosclerosis in Hong Kong Chinese. Severity in intracranial and extracranial vessels

BACKGROUND AND PURPOSE

The clinical pattern of stroke and the angiographic distribution of cerebral atherosclerosis in Chinese are different from those in Caucasians. Pathological data from autopsy studies are lacking.

METHODS

The intracranial and extracranial arteries supplying the brains of 114 consecutive Chinese patients undergoing autopsy in a regional general hospital were examined by computer-assisted morphometric analysis under a microscope as well as by macroscopic grading for atherosclerotic narrowing. The severity was correlated with various atherosclerosis-related factors.

RESULTS

Atherosclerosis of the intracranial cerebral vessels was more severe than that of the extracranial vessels. The distal branches of the intracranial vessels were also commonly involved. Hypertension and diabetes mellitus were identified as factors associated only with intracranial atherosclerosis (p < 0.001), whereas ischemic heart disease was associated with atherosclerosis in both the intracranial (p < 0.001) and extracranial (p = 0.012) vessels. Smoking was associated with narrowing of the extracranial vessels only (p = 0.0054).

CONCLUSIONS

Compared with figures from Caucasian and Japanese populations, the extent of intracranial atherosclerosis is much more severe in Hong Kong Chinese, whereas atherosclerotic narrowing of the extracranial carotid artery is less severe in Hong Kong Chinese than in Caucasians.

Impact of apolipoprotein E polymorphism in determining interindividual variation in total cholesterol and low density lipoprotein cholesterol in Hispanics and non-Hispanic whites

The extent of apolipoprotein E (apo E) polymorphism and its effect on eight quantitative risk factors for coronary heart disease (total cholesterol; low density lipoprotein (LDL) cholesterol; total high density lipoprotein and its subfractions, HDL2 and HDL3; triglycerides; fasting glucose and fasting insulin) has been determined in 238 randomly selected Hispanics (120 males and 118 females) and 201 non-Hispanic whites (NHWs) (105 males and 96 females) from the San Luis Valley, Colorado. The frequencies for the E * 2, E * 3 and E * 4 alleles were 0.048, 0.853 and 0.099, respectively, in Hispanics and 0.080, 0.783 and 0.137, respectively, in NHWs. Relatively low frequency of the E * 2 and E * 4 alleles in Hispanics compared with NHWs is consistent with the genetic and anthropologic data that Hispanics have substantial Amerindian admixture. The impact of apo E polymorphism on each quantitative trait was estimated after adjusting for concomitant variables including age, cigarette smoking and body mass index in both genders and pre- or post-menopause status in females. The distribution of eight quantitative traits was analyzed among three common apo E phenotypes, 3-2, 3-3 and 4-3. In Hispanics, significant variability among apo E phenotypes was observed for total cholesterol (P = 0.001) in females only and the apo E polymorphism accounts for 12.4% variation in total cholesterol and 15.2% variation in LDL-cholesterol. In NHWs, significant mean differences among apo E phenotypes were observed for total cholesterol in both males (P = 0.007) and females (P = 0.0004). In NHW males and females, the apo E polymorphism explained 9.2% and 12.4%, respectively, of the variation in total cholesterol, and 15.1% and 6.6%, respectively, of the variation in LDL-cholesterol. In NHWs, borderline significance levels were also noted for phenotype specific differences in HDL2-cholesterol in males (P = 0.04) and females (P = 0.05), for total HDL cholesterol in females (P = 0.02) and HDL3-cholesterol in females (P = 0.06). While the estimated effects of the apo E polymorphism on quantitative traits differ somewhat between Hispanics and non-Hispanic whites, this probably reflects the overall difference in frequencies of the less common alleles in the Hispanics rather than a biological difference in the effects of these alleles on lipid metabolism.

Gene-environment interactions in atherosclerosis

The importance of environment and genetics working together to shape an individual's risk for atherosclerosis seems intuitively obvious. However, it is only recently that research strategies have begun to evolve that attempt to answer questions related to apportionment of risk that is due to specific environmental and genetic factors. These factors may impact upon risk either singly or, more likely, through a complex interaction that affects the metabolic history of the whole organism. Because the genetic bases of lipid and lipoprotein metabolism have been well-studied, and because of the epidemiologic and pathobiochemical associations between genetic disorders of lipid metabolism and atherosclerosis, researchers have searched for gene-environment interactions within animal and human systems in which the phenotype is defined by some index of lipoprotein metabolism. From work done in the lipoprotein area to this point a clear case can be made for: 1) the genetic influence over the phenotypic response to an environmental stimulus; 2) the environmental modulation of the phenotypic expression of severe genetic defects. In the realm of gene-environment interactions that affect lipoprotein phenotype, diet is the best-studied environmental factor.

Association of apolipoprotein B gene variants with plasma apoB and low density lipoprotein (LDL) cholesterol levels

The contribution of the variants of the apolipoprotein (apo) B locus to the total variance in plasma apoB and cholesterol levels was examined in four independent populations, two that were composed of normal controls (n = 77 and 85) and two with coronary heart disease (n = 115 and 159). A correlation between genotype at the apoB-XbaI locus and apoB levels was observed. The effects of the (+; presence of restriction site) and (-) alleles were to increase or decrease the apoB and cholesterol levels by approximately 3.5 mg/dl, respectively. None of the 274 individuals in the coronary heart disease (CHD) groups was found to be a carrier of the apoB allele Arg3500----Gln, previously shown to be associated with an apoB protein defective in binding to the low density lipoprotein receptor (LDL-R). No DNA sequence variants were found in the region encoding amino acid residues 3129-3532 within the putative LDL-R binding domain among 35 individuals with apoB levels above the 94th percentile (141 mg/dl).

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

The impact of the common alleles at structural loci coding for apolipoprotein (apos) A-IV, E, and H on 12 quantitative risk factors for cardiovascular disease (apos A-I, A-II, B, C-II, C-III, and E; total cholesterol; triglycerides; high density lipoprotein cholesterol; systolic blood pressure; diastolic blood pressure; and red blood cell sodium-lithium countertransport) was estimated in 453 unrelated individuals (227 men and 226 women) aged 26-63 years from the Rochester Family Heart Study, who were not using medications affecting lipid levels or blood pressure. Each risk factor was adjusted for concomitants (assay date, age, age, squared, height, weight and smoking status) before the genotypic effects on mean levels and variances were estimated. Allele frequencies were the same in men and women and were similar to those observed in other studies of US Caucasians. There were very different gender-specific estimates of the relative contribution of concomitants, measured genetic effects, and residual unexplained effects to the interindividual variation of particular traits. Allelic variation in apo E had effects on the greatest number of traits, namely apo E, apo B, apo C-II, and total cholesterol. An effect on triglycerides was dependent on the inclusion of hypertriglyceridemic subjects. Allelic effects of apo A-IV and apo H were much less than those estimated for the apo E polymorphism. A possible role for apo H in high density lipoprotein metabolism is suggested. This study indicates that variation in many genes may influence variation in a particular trait and that a particular gene may have pleiotropic effects on several traits.

DNA restriction polymorphisms of the apolipoprotein AI-CIII-AIV gene cluster: a genetic determinant of atherosclerosis in type 2 (non-insulin-dependent) diabetes mellitus

The presence of polymorphic restriction sites (S2, M2, P2) of the apolipoprotein AI-CIII-AIV gene cluster for the respective Sst1, Msp1, and Pst1 enzymes was assessed after hybridization with a radiolabelled apolipoprotein AI gene probe in 64 Type 2 diabetic patients and 67 healthy control subjects, all Europids. Twenty-two diabetic patients showed evidence of ischaemic heart disease or macrovascular arteriopathy and forty-two were free of cardiovascular complications. Control subjects were selected for the absence of personal or familial metabolic or cardiovascular diseases. The frequencies of polymorphic alleles were in agreement with previous studies in the control group: S2 6.3 (95% confidence interval (CI) 2.3-10.3) %, M2 5.5 (1.6-9.4) %, P2 6.3 (2.3-10.3) % and did not differ in the whole diabetic group: S2 4.2 (0.7-7.7) %, M2 6.5 (2.0-11.0) %, P2 6.6 (2.3-10.9) %. The relative prevalences of S2, M2, and P2 alleles were, respectively: 3.32, 1.54, and 2.00 (Woolf's ratio) in the macroangiopathic group but allele distribution frequencies were not statistically different from non-macroangiopathic patients. The allelic associations S2M2P1 and S1M1P2 showed a relative prevalence of 2.86 and 2.00 in the presence of cardiovascular complications but the difference was not significant in terms of polyallelic distribution frequencies in the absence of atherosclerosis. No serum lipid abnormalities could be related to the presence of any polymorphic allele or allelic association. These results suggest a genetic influence on the development of atherosclerosis in Type 2 diabetes, but the mechanism remains unclear.

Effects of the apolipoprotein E polymorphism on levels of lipids, lipoproteins, and apolipoproteins among Mexican-Americans in Starr County, Texas

Genetic variability has been implicated as a significant contributor to the variation in levels of lipids, lipoproteins, and apolipoproteins (apos) through a variety of direct and indirect investigations. Among the direct investigations, apo E has been shown to be polymorphic and to explain a small but statistically significant proportion of the variability in cholesterol. The apo E polymorphism was typed in 964 randomly selected Mexican-Americans from Starr County, Tex., and its effects determined on levels of cholesterol, triglycerides, total high density lipoprotein (HDL) cholesterol, subfractions (HDL2 and HDL3), alpha- and beta-lipoprotein cholesterol, low density lipoprotein (LDL) cholesterol, and apos A-I, A-II, B, C-II, C-III, and E. Effects are reported for the entire sample and in each of three groups, namely, premenopausal females, postmenopausal women, and males. In the entire sample, significant effects were observed on cholesterol, beta-lipoprotein cholesterol, LDL, apo B, and apo E. There is evidence for significant physiological interaction of the apo E polymorphism effect in females by menopausal status. This is most evident for apo E levels, in which 5.9% of the variability in the entire sample is explained by the apo E polymorphism. In premenopausal females, however, the polymorphism accounts for 27.5% of the variability. In postmenopausal women and males, there is no significant effect. It is shown that the apo E polymorphism can be treated as a two-locus, two-allele system. Doing so identifies substitutions in amino acid position 158 as the mediators of most of the observed effects of this polymorphism.

Genetic studies of human apolipoproteins. XVII: Population genetics of apolipoprotein polymorphisms in American Samoa

Variation in human apolipoprotein genes is a major source of phenotypic differences in human lipid metabolism. Data regarding genetic variation at apolipoprotein loci in various populations are only beginning to accumulate, and they suggest that different populations vary widely in distribution of apolipoprotein alleles. Using isoelectric focusing-immunoblotting techniques, we screened 67 serum samples from self-identified Samoan residents of American Samoa to investigate structural variation at six apolipoprotein loci: A-I, A-II, A-IV, C-II, E, and H. The APO A-I, A-II, and C-II loci were found to be monomorphic by isoelectrical focusing. In Samoans, the common three-allele polymorphism was observed for APO E, with no striking differences in frequencies from Caucasian populations. The three common alleles of the APO H locus also were identified; however, frequencies of the less common alleles (APO H*I and APO H*3) were different from those observed elsewhere for Caucasians.

The hyperlipoproteinemias

The association of disturbances of plasma lipid transport and atherogenesis has been recognized, and scientific data continue to accumulate to explain this association from a mechanistic viewpoint. A number of recent clinical trials have shown that cholesterol-lowering therapy can prevent the complications of atherosclerosis. Consequently, the attention of physicians to therapeutic intervention has increased and public awareness to plasma cholesterol levels has been heightened. This article summarizes current knowledge of how plasma lipid transport is regulated. The classical primary hyperlipoproteinemias are considered and hyperlipoproteinemias occurring secondary to other diseases are discussed. Standard methods to diagnose the defined genetic hyperlipidemias are outlined, and new approaches to assess risk of atherosclerosis are examined. Finally, the role of dietary measures and drugs in lowering blood lipids and reducing risk of coronary heart disease is delineated.

Phenotypic effects of apolipoprotein structural variation on lipid profiles: II. Apolipoprotein A-IV and quantitative lipid measures in the healthy women study

Apolipoprotein A-IV (APO A-IV) is a major protein component of mesenteric lymph chylomicrons and very-low-density lipoproteins. It is found in plasma predominantly unassociated with major lipoprotein fractions and in high density lipoproteins. APO A-IV exhibits structural heterogeneity owing to two codominant alleles, APO A-IV*1 and APO A-IV*2, that occur in Caucasian and black populations. In vitro experimental evidence indicates that APO A-IV may be a cofactor for the lecithin:cholesterol acyltransferase enzyme, may be involved in reverse cholesterol transport, and may play an important role in the modulation of lipoprotein lipase activity. In this study we have investigated the effect of two APO A-IV phenotypes, APO A-IV 1-1 and APO A-IV 2-1, on quantitative lipid measures in a group of 453 white women being followed through menopause for changes in cardiovascular risk. At baseline all women were premenopausal. Of the nine lipid measures, triglycerides showed a marginally significant effect caused by phenotype. The APO A-IV 2-1 heterozygotes had lower average triglycerides than the 1-1 homozygotes (P = .053).

Rapid typing of tandemly repeated hypervariable loci by the polymerase chain reaction: application to the apolipoprotein B 3' hypervariable region

The 3' flanking region of the apolipoprotein B (apoB) gene contains a hypervariable region consisting of a variable number of tandemly repeated short A + T-rich DNA sequences (VNTRs). We present a general method that utilizes the polymerase chain reaction to rapidly and accurately type this and other VNTR loci. We use tailored oligonucleotides and thermostable Taq polymerase to amplify the targeted region. The amplification products are directly visualized after agarose gel electrophoresis. Twelve alleles were readily identified in a sample of 125 unrelated individuals. The alleles differ with respect to the length of the amplified gene region. This genetic variability is inherited in an autosomal codominant manner. DNA sequence data indicate that individual alleles differ in the number of repeat units and the sensitivity of the technique is such that alleles differing in length by only 32 base pairs are readily distinguishable. A system of nomenclature based on the number of repeat units is suggested; an allele containing 37 repeat units is designated 3' beta 37, one containing 35 units is 3' beta 35, and so on. The frequency distribution of the 12 apoB VNTR alleles is bimodal with peaks at 37 and 47 repeat units and a nadir near 43 repeat units. We estimate that the 3' apoB VNTR locus has a heterozygosity index of 0.75 and a polymorphic information content of 0.73. It is a highly informative marker for genetic linkage studies on chromosome 2 and clinical and epidemiological studies involving the apoB gene. The high sensitivity and inexpensive nature of this technique make it superior to traditional Southern blot analysis for typing the 3' apoB VNTR. The method described is also directly applicable for rapid typing of other VNTRs in the human genome.

Apolipoprotein E alleles and hyperlipoproteinemia in Japan

Genetic polymorphism of apolipoprotein (apo) E has been demonstrated to be associated with hyperlipoproteinemia (HLP). There are few reports on this association in Japan. Thus, in this study, we have examined the apo E allele frequencies in normolipidemia (n = 129), non-familial hypercholesterolemic (FH) type IIa HLP (n = 40), non-FH type IIb HLP (n = 35), type III HLP (n = 17), type IV HLP (n = 59), type V HLP (n = 19) and heterozygous FH (n = 51) in Japan, and compared these frequencies between normolipidemia, and different types of HLP and FH. The frequency of the epsilon 4 allele was significantly higher in type IIa (18.7%), IIb (21.4%) and V (29.0%) HLP and FH (16.6%) than in normolipidemia (8.9%), whereas the frequency of the epsilon 2 allele was significantly higher in type III (70.6%) and IV (11.0%) HLP than in normolipidemia (3.1%). These results indicate that the epsilon 4 allele is associated with non-FH hypercholesterolemia (type IIa and IIb HLP), type V HLP and FH, whereas the epsilon 2 allele is associated not only with type III HLP but also with type IV HLP.

Familial hypercholesterolemia and apolipoprotein E4

The purpose of this study was to elucidate the relationship between two genetic factors associated with raised blood cholesterol, i.e. familial hypercholesterolemia (FH) and apolipoprotein (apo) E4. A group of 50 unrelated heterozygous FH patients aged 33-71 years were studied together with 129 normolipidemic subjects. A significantly higher frequency of apo E4 phenotypes was found in FH patients (30.0%) than in normolipidemic subjects (15.5%). FH patients were divided into two groups with and without apo E4. Plasma total cholesterol (Chol) and triglyceride (TG) levels were significantly higher, and plasma low density lipoprotein-cholesterol (LDL-Chol) level tended to be higher in FH patients with apo E4 than in those without apo E4. In addition, the prevalence of ischemic heart disease (IHD) was significantly higher in FH patients with apo E4 (73.3%) than in those without apo E4 (31.4%). No significant difference was noted in age and in the prevalence of obesity, diabetes, hypertension and smoking between the FH groups with and without apo E4. These results suggest that apo E4 is associated with higher levels of total Chol and TG and, at least in part, contributes to the predisposition to IHD in FH.