Serum low density lipoprotein cholesterol level and cholesterol absorption efficiency are influenced by apolipoprotein B and E polymorphism and by the FH-Helsinki mutation of the low density lipoprotein receptor gene in familial hypercholesterolemia

Plasma Non-cholesterol Sterols as Markers of Cholesterol Synthesis and Intestinal Absorption: A Critical Review

Plasma concentrations of phytosterols and non-cholesterol sterol precursors of cholesterol synthesis have been used as markers of intestinal cholesterol absorption and synthesis in inherited and secondary dyslipidemias and in population-based investigations to evaluate the risk for cardiovascular disease, respectively. The method aims at replacing initial research procedures such as the use of stable isotopes associated with fecal steroid balance, which are limited by the high cost and tedious procedures. However, we show in this review that numerous results obtained with serum sterol measurements are contradictory. In this regard, the following points are discussed: 1) how phytosterols relate to atherosclerosis considering that defects in biliary output or in the transport of phytosterols from the intestinal mucosa back into the intestinal lumen provide increased content of phytosterols and other sterols in plasma and tissues, thus not allowing to conclude that their presence in arteries and atheromas represents the etiology of atherosclerosis; 2) serum non-cholesterol sterols as markers of cholesterol synthesis and absorption, such as cholestanol, present discrepant results, rendering them often inadequate to identify cases of coronary artery disease as well as alterations in the whole body cholesterol metabolism; 3) such methods of measurement of cholesterol metabolism are confounded by factors like diabetes mellitus, body weight and other pathologies including considerable hereditary hyperlipidemias biological variabilities that influence the efficiency of synthesis and intestinal absorption of cholesterol.

Molecular Characterization of Familial Hypercholesterolemia in a North American Cohort

Background

Familial hypercholesterolemia (FH) confers a very high risk of premature cardiovascular disease and is commonly caused by mutations in low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), or proprotein convertase subtilisin/kexin type 9 (PCSK9) and very rarely in LDLR adaptor protein 1 (LDLRAP1) genes.

Objective

To determine the prevalence of pathogenic mutations in the LDLR, APOB, and PCSK9 in a cohort of subjects who met Simon Broome criteria for FH and compare the clinical characteristics of mutation-positive and mutation-negative subjects.

Methods

Ninety-three men and 107 women aged 19 to 80 years from lipid clinics in the United States and Canada participated. Demographic and historical data were collected, physical examination performed, and serum lipids/lipoproteins analyzed. Targeted sequencing analyses of LDLR and PCSK9 coding regions and exon 26 of APOB were performed followed by detection of LDLR deletions and duplications.

Results

Disease-causing LDLR and APOB variants were identified in 114 and 6 subjects, respectively. Of the 58 LDLR variants, 8 were novel mutations. Compared with mutation-positive subjects, mutation-negative subjects were older (mean 49 years vs 57 years, respectively) and had a higher proportion of African Americans (1% vs 12.5%), higher prevalence of hypertension (21% vs 46%), and higher serum triglycerides (median 86 mg/dL vs 122 mg/dL) levels.

Conclusions

LDLR mutations were the most common cause of heterozygous FH in this North American cohort. A strikingly high proportion of FH subjects (40%) lacked mutations in known culprit genes. Identification of underlying genetic and environmental factors in mutation-negative patients is important to further our understanding of the metabolic basis of FH and other forms of severe hypercholesterolemia.

Longitudinal trajectories of cholesterol from midlife through late life according to apolipoprotein E allele status

BACKGROUND

Previous research indicates that total cholesterol levels increase with age during young adulthood and middle age and decline with age later in life. This is attributed to changes in diet, body composition, medication use, physical activity, and hormone levels. In the current study we utilized data from the Framingham Heart Study Original Cohort to determine if variations in apolipoprotein E (APOE), a gene involved in regulating cholesterol homeostasis, influence trajectories of total cholesterol, HDL cholesterol, and total: HDL cholesterol ratio from midlife through late life.

METHODS

Cholesterol trajectories from midlife through late life were modeled using generalized additive mixed models and mixed-effects regression models.

RESULTS

APOE e2+ subjects had lower total cholesterol levels, higher HDL cholesterol levels, and lower total: HDL cholesterol ratios from midlife to late life compared to APOE e3 and APOE e4+ subjects. Statistically significant differences in life span cholesterol trajectories according to gender and use of cholesterol-lowering medications were also detected.

CONCLUSION

The findings from this research provide evidence that variations in APOE modify trajectories of serum cholesterol from midlife to late life. In order to efficiently modify cholesterol through the life span, it is important to take into account APOE allele status.

APOE and FABP2 Polymorphisms and History of Myocardial Infarction, Stroke, Diabetes, and Gallbladder Disease

Dysfunctional lipid metabolism plays a central role in pathogenesis of major chronic diseases, and genetic factors are important determinants of individual lipid profiles. We analyzed the associations of two well-established functional polymorphisms (FABP2 A54T and APOE isoforms) with past and family histories of 1492 population samples. FABP2-T54 allele was associated with an increased risk of past history of myocardial infarction (odds ratio (OR) = 1.51). Likewise, the subjects with APOE4, compared with E2 and E3, had a significantly increased risk of past history myocardial infarction (OR = 1.89). The OR associated with APOE4 was specifically increased in women for past history of myocardial infarction but decreased for gallstone disease. Interactions between gender and APOE isoforms were also significant or marginally significant for these two conditions. FABP2-T54 allele may be a potential genetic marker for myocardial infarction, and APOE4 may exert sex-dependent effects on myocardial infarction and gallbladder disease.

Functional polymorphisms to modulate luminal lipid exposure and risk of colorectal cancer

PURPOSE

Fat absorption may play a crucial role in colorectal carcinogenesis by determining intra-colonic exposure to potentially carcinogenic lipid metabolites.

METHODS

We conducted a population-based case-control study that included 1163 cases and 1501 controls to examine whether individuals who carry genetic variants associated with lower lipid absorption have a higher risk of colorectal cancer. Using Taqman assay, we determined FABP2 alanine (A)/threonine (T) polymorphism at codon 54 in exon-2 and APOE isoforms. Multivariable odds ratios (OR) and 95% confidence intervals (CI) were calculated by unconditional logistic regression models, assuming FABP2 A54 and APO non-E4 as high risk alleles.

RESULTS

We found no associations with either of the polymorphisms. The OR associated with FABP2 A54 homozygotes compared with the others was 1.01 (95% CI; 0.86-1.45) and that for non-ApoE4 carriers compared with carries was 0.95 (95% CI; 0.80-1.13). However, there was a statistically significant negative interaction between total fat intake and FABP2 AA genotypes (p=0.025), indicating that the risk of colorectal cancer associated with this polymorphism is higher in the subjects with lower fat intake.

CONCLUSIONS

These results suggest that these SNPs may not be useful in predicting colorectal cancer risk in populations with high fat intake.

Effects of ezetimibe on lipids and lipoproteins in patients with hypercholesterolemia and different apolipoprotein E genotypes

BACKGROUND

The epsilon4 allele of the gene encoding apolipoprotein E (apoE) is associated with elevated serum levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C), as well as an increased risk of coronary heart disease (CHD), greater disease severity, and higher CHD mortality. ApoE epsilon4 allele carriers have also shown reduced lipid and lipoprotein responses to lipid-modifying pharmacotherapy and lifestyle modifications.

OBJECTIVE

To provide preliminary descriptive data on the effects of apoE genotype on lipid and lipoprotein responses to the cholesterol absorption inhibitor ezetimibe (Ezetrol/Zetia) in Hungarian subjects not at cholesterol goals at baseline.

METHODS

This prospective open-label study compared the effects of the cholesterol absorption inhibitor ezetimibe 10 mg/day for up to 6 weeks added to existing therapies on the lipid profiles of 14 epsilon4 allele carriers and 14 age- and gender-matched APOE3/APOE3 homozygotes.

RESULTS

Treatment with ezetimibe reduced TC, LDL-, and triglycerides, and increased high-density lipoprotein cholesterol (HDL-) significantly from baseline, and to similar extents, in both groups, lowering TC from baseline by 13.7% in APOE3/APOE3 homozygotes compared with 12.1% in epsilon4 allele carriers (p = 0.139); LDL-C by 22.8% (vs. 19.6%; p = 0.081); and triglycerides by 9.2% (vs. 9.1%; p = 0.120). Ezetimibe also increased HDL-C by 8.0% in subjects with the epsilon3/epsilon3 genotype compared with 8.9% in epsilon4 allele carriers (p = 0.263).

CONCLUSIONS

Ezetimibe significantly improved lipid and lipoprotein profiles from baseline irrespective of apoE epsilon3/epsilon3 or epsilon4 genotype in Hungarian subjects not at cholesterol goals. Limitations of our study include its open-label nature and small sample population, as well as the facts that patients with the epsilon4 allele were not included and data were not collected on initial cholesterol levels, initial statin doses, cholesterol responses to statins, and the safety and tolerability of ezetimibe. Further randomized controlled studies in larger numbers of people followed for longer intervals are warranted to confirm these findings.

Guidelines for the diagnosis and management of heterozygous familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism characterized by very high plasma concentrations of low density lipoprotein cholesterol (LDLc), tendon xanthomas and increased risk of premature coronary heart disease (CHD). FH is a public health problem throughout the world. There are 10,000,000 people with FH worldwide, mainly heterozygotes, and approximately 85% of males and 50% of females with FH will suffer a coronary event before 65 years old if appropriate preventive efforts are not implemented. Early identification of persons with FH and their relatives, and the early start of treatment are essential issues in the prevention of premature cardiovascular disease (CVD) and death in this population. However, guidelines for the general population formally exclude FH from their diagnostic and treatment recommendations. These guidelines have been elaborated by a group of international experts with the intention to answer the main questions about heterozygous FH (heFH) subjects that physicians worldwide face in the diagnosis and management of these patients.

Apolipoprotein E genotype is not associated with cardiovascular disease in heterozygous subjects with familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is a genetic disorder characterized by high low-density lipoprotein cholesterol levels and premature cardiovascular disease (CVD). There are important differences in the presence of CVD among heterozygous subjects with FH. Some of this variability can be explained by genetic factors, and the apolipoprotein (apo) E genotype has been proposed as a useful marker.

METHODS

We analyzed the apo E genotype in 706 non-related subjects who were heterozygous for FH from Spain. CVD was present in 198 subjects (28%), 132 men (41%) and 66 women (17%).

RESULTS

Apo E allele frequencies for the epsilon 3, epsilon 4, and epsilon 2 alleles were 0.89, 0.09, and 0.02 respectively. Age, body mass index, smoking status, high blood pressure, diabetes mellitus, presence of tendon xanthomas, total cholesterol level, triglyceride levels, high-density lipoprotein cholesterol level, low-density lipoprotein cholesterol level, and Lp(a) did not differ among genotypes. The incidence of CVD and the age of onset of CVD did not differ among genotypes either. In the multivariant analysis, apo E genotype did not contribute significantly to CVD.

CONCLUSIONS

Heterozygous men with FH have a very high risk of coronary disease in a Mediterranean country, and the apo E genotype in this large group of adults with FH is not associated either with CVD or lipid values, in contrast with the established effect in the general population.

Carotid intima-media thickness and plaque in patients with familial hypercholesterolaemia mutations and control subjects

BACKGROUND

In individuals with familial hypercholesterolaemia (FH), ultrasonographic measurement of carotid intima-media thickness (IMT) and plaque may provide a non-invasive assessment of cardiovascular risk.

METHODS

We examined carotid artery IMT and its determinants in 79 non-smoking, normotensive, treated men and women with FH aged 26-46 years, and in 79 non-smoking, normotensive sex-, age- and body mass index-matched control subjects. FH was verified by molecular genetic analyses. The underlying mutation in the low-destiny lipoprotein receptor gene included a splice-site mutation, mutations predicted or shown to lead to class 2B mutations or other mutations that probably represent class I mutations (null alleles).

RESULTS

The carotid bifurcation and common carotid artery IMT was increased in men with FH compared with control subjects (0.81 +/- 0.15 mm vs. 0.74 +/- 0.19 mm and 0.61 +/- 0.13 mm vs. 0.55 +/- 0.14 mm respectively; P < 0.05). The carotid bifurcation IMT was increased in women with FH compared with control subjects (0.74 +/- 0.17 vs. 0. 66 +/- 0.15; P = 0.005). More subjects with FH had carotid plaque (54% vs. 14%; P = 0.0001). In multivariate analysis, male gender, level of low-density lipoprotein-cholesterol, cholesterol-years score and xanthoma were associated with IMT and plaque in subjects with FH. FH subjects with class 2B mutations had lower cholesterol levels than subjects with mutations belonging to the other classes. They also had a tendency towards a decreased common carotid artery IMT.

CONCLUSION

These findings confirm the importance of gender, xanthoma and lifetime cholesterol levels in relation to carotid atherosclerosis in FH. Whether the type of mutation causing FH modulates carotid artery IMT and plaque requires further study.

Familial hypercholesterolemia: potential diagnostic value of mutation screening in a pediatric population of South Africa

Three founder-related low-density lipoprotein receptor (LDLR) gene mutations, D154N, D206E and V408M, cause familial hypercholesterolemia (FH) in approximately 90% of South African Afrikaners. Two hundred and twenty-one South African children, from 85 affected families, were screened for the specific mutation identified previously in the index case. Sixty boys and 56 girls were heterozygous for mutation D154N (FH3), D206E (FH1) or V408M (FH2). Total and LDL cholesterol (LDLC) levels were similar among the children heterozygous for the three founder mutations, and mean values were significantly higher compared to those without a known mutation (p < 0.0001). Plasma cholesterol levels overlapped considerably between the different groups, suggesting that modifiable lifestyle factors remain important in children with FH. This study demonstrates the potential diagnostic value of mutation screening in a pediatric population with an enrichment of particular gene mutations.

Heritability of longitudinal changes in coronary-heart-disease risk factors in women twins

Numerous studies have demonstrated genetic influences on levels of coronary heart disease (CHD) risk factors, but there also may be genetic effects on the intraindividual variation in these risk factors over time. Changes in risk factors are likely to reflect genetic-environmental interactions and may have important implications for understanding CHD risk. The present study examines the heritability of changes in CHD risk factors, using data from the two examinations by the Kaiser Permanente Women Twins Study, performed a decade apart. The sample consisted of 348 pairs of women twins who participated in both examinations, including 203 MZ pairs and 145 DZ pairs. Average ages at the two examinations were 41 and 51 years, respectively. By means of three different statistical analytic approaches, moderate heritability estimates were demonstrated for changes in LDL cholesterol (h2 = .25-.36) and in HDL cholesterol (h2 = .23-.58), some of which were statistically significant. Although small to moderate heritability estimates were found for systolic blood pressure (.18-.37; P < .05 for some estimates), no genetic influence on changes in diastolic blood pressure was detected. Based on longitudinal twin data in women, this study demonstrates a genetic influence on changes in both lipoprotein risk factors and systolic blood pressure over a decade. In addition to environmental factors, which clearly are operating, the effect of various "variability genes" may be acting independently of the genetic influences on the absolute levels of these risk factors. Both mapping the gene(s) underlying intraindividual variations in these CHD risk factors and understanding their function(s) could lead to targeted intervention strategies to reduce CHD risk among genetically susceptible individuals.

A novel single base deletion in the LDLR gene (211delG): Effect on serum lipid profiles and the influence of other genetic polymorphisms in the ACE, APOE and APOB genes

A single base deletion (211delG) in the low density lipoprotein receptor (LDLR) gene was shown to cause familial hypercholesterolaemia (FH) in a large family from Northern Ireland. Twenty-four of 52 family members tested had this mutation, 13 of which were newly diagnosed. Mutation-positive individuals had significantly higher mean total-cholesterol (TC) and LDL-cholesterol (LDL-C) than those without 211delG. LDL-C was a more accurate indicator of disease status than TC. When TC levels alone were considered, in individuals over 16 years, a false negative rate (TC < 7.5 mmol/l) of 40% was found; however this fell to 13% based on inclusion of LDL-C levels. Individuals with coronary artery disease (CAD) had significantly higher TC levels than those without CAD and tended to have tendinous xanthomas (TX) and corneal arcus (CA). Generic polymorphisms in the angiotensin converting enzyme (ACE) and apolipoprotein (apo) B genes did not appear to be associated with lipid levels or with the clinical severity of the disease; however, the apo E epsilon4 allele did show a lipid-raising effect in individuals with the mutation.

Influence of apolipoprotein E genotypes on plasma lipid and lipoprotein concentrations: results from a segregation analysis in pedigrees with molecularly defined familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a monogenic disorder caused by mutations in the low-density lipoprotein (LDL) receptor gene. Large variations in plasma lipids and lipoprotein levels have been observed in FH families. These may be caused by other environmental and genetic factors of which apolipoprotein E (apo E) is a candidate. The possible influence of apo E polymorphism on components of variation in plasma LDL-C, triglycerides, high-density lipoprotein cholesterol (HDL-C), and lipoprotein(a) (Lp(a)) levels was investigated in 235 members of 14 families with FH. Sex-and age-adjusted mean LDL-C was influenced significantly by the apo E genotype in non-FH subjects (P <or= .01), and a similar trend was observed in FH cases. Mean plasma levels of triglyceride, HDL-C, and Lp(a) were not significantly different across the apo E genotypes in FH and in non-FH family members. Complex segregation analysis was first applied to these sex- and age-adjusted data. In addition to the major gene involved in LDL-C levels (i.e., the LDL receptor gene), there was evidence for a non-transmitted environmental major factor in addition to polygenic effect that explained the mixture of distributions in TG and a major effect in addition to polygenic loci which influenced Lp(a) levels. There was no evidence for a single major factor controlling HDL-C levels in these pedigrees. When the segregation models allowed apo E regression coefficients to be ousiotype (class) specific, the results suggested that apo E genotypes have a significant effect on LDL-C, TG, and Lp(a) levels. In conclusion, the analysis presented here supports the concept that the apo E gene has an important role in the regulation of plasma lipid and lipoproteins in FH.

Apolipoprotein E competitively inhibits receptor-dependent low density lipoprotein uptake by the liver but has no effect on cholesterol absorption or synthesis in the mouse

This study examines the question of whether apolipoprotein E (apoE) alters steady-state concentrations of plasma cholesterol carried in low density lipoproteins (LDL-C) by acting as a competitive inhibitor of hepatic LDL uptake or by altering the rate of net cholesterol delivery from the intestinal lumen to the liver. To differentiate between these two possibilities, rates of cholesterol absorption and synthesis and the kinetics of hepatic LDL-C transport were measured in vivo in mice with either normal (apoE+/+) or zero (apoE-/-) levels of circulating apoE. Rates of cholesterol absorption were essentially identical in both genotypes and equaled approximately 44% of the daily dietary load of cholesterol. This finding was consistent with the further observation that the rates of cholesterol synthesis in the liver (approximately 2,000 nmol/h) and extrahepatic tissues (approximately 3,000 nmol/h) were also essentially identical in the two groups of mice. However, the apparent Michaelis constant for receptor-dependent hepatic LDL-C uptake was markedly lower in the apoE-/- mice (44 +/- 4 mg/dl) than in the apoE+/+ animals (329 +/- 77 mg/dl) even though the maximal transport velocity for this uptake process was essentially the same (approximately 400 micrograms/h per g) in the two groups of mice. These studies, therefore, demonstrate that apoE-containing lipoproteins can act as potent competitive inhibitors of hepatic LDL-C transport and so can significantly increase steady-state plasma LDL-C levels. This apolipoprotein plays no role, however, in the regulation of cholesterol absorption, sterol biosynthesis, or hepatic LDL receptor number, at least in the mouse.

Cholesterol absorption and metabolism and LDL kinetics in healthy men with different apoprotein E phenotypes and apoprotein B Xba I and LDL receptor Pvu II genotypes

Apoprotein (apo) E, apoB Xba I, and LDL receptor gene Pvu II polymorphisms are associated with LDL cholesterol level, but little is known about cholesterol and LDL metabolism in subjects with the latter two genetic polymorphisms alone or in combination with different apoE phenotypes. We studied cholesterol absorption efficiency, cholesterol and bile acid synthesis, and LDL apoB kinetics in 52 healthy men and related the metabolic results to the apoB Xba I and LDL receptor Pvu II restriction fragment length polymorphism (RFLP) and apoE phenotypes. New findings were as follows. ApoB Xba I polymorphism was not associated with the metabolic variables of cholesterol, but LDL receptor Pvu II RFLP was associated with fractional catabolic rate for LDL apoB, cholesterol absorption, and cholesterol and bile acid synthesis. ApoE polymorphism exerted the most powerful effect on the LDL cholesterol concentration, so that the apoE2 subjects had the lowest LDL cholesterol and apoB levels and cholesterol absorption, and the highest fractional catabolic rate and bile acid and cholesterol synthesis compared with the apoE3 or especially apoE4 phenotypes in different genetic combinations. In multiple stepwise regression analysis with LDL cholesterol as the dependent and the genetic and metabolic parameters as the independent variables, 47.0% (n = 35, P < .001) of the variability of LDL cholesterol was explained by the apoE polymorphism, 7.1% (P < .05) by the LDL receptor Pvu II RFLP, and 11.3% (P < .01) by bile acid synthesis, while the contribution of the apoB Xba I RFLP was nonsignificant.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma lipids and lipoproteins response to a dietary challenge: analysis of four candidate genes

The possible role of four candidate genes in lipid and lipoprotein response to diet was examined in 63 male students. Four site polymorphisms (signal peptide insertion/deletion, XbaI, MspI and EcoRI) of the apo B gene, three RFLPs (AvaII, StuI, and HincII) of the LDL receptor gene, two SSCPs of the cholesterol 7 alpha-hydroxylase gene and the common apo E genotypes were determined. The average reductions induced by diet in participants homozygous for the absence of the XbaI restriction site (X-X-) of the apo B gene compared to those harboring this site (X+) were: 14.5 mg/dl and 9.4 mg/dl for total cholesterol (TC) (p < 0.09) and 15.5 mg/dl and 7.9 mg/dl for LDL-C (p < 0.003), respectively. Differences in dietary responsiveness among the apo E, LDL receptor and the cholesterol 7 alpha-hydroxylase genotypes were largely insignificant. Using the four apo B polymorphic sites, six unambiguous haplotypes were constructed and a model for their possible evolutionary relationship is presented. Genetic variation in the apo B gene region, as defined by haplotypes, accounted for 8.7% and 24.3% of the phenotypic variance in TC and LDL-C response to diet, respectively. Sequence analysis of a candidate locus, the putative LDL receptor binding region of apo B and its flanking sequences, was performed in two individuals, one homozygous for an apo B "hyper-responding" and another for the "lower-responding" haplotype, and no differences were found. In conclusion, haplotypes at the apo B gene locus are associated with dietary response of TC and LDL-C in young males. Yet, the sequence variation responsible for these differences is possibly located outside the putative LDL receptor binding domain.

Phenotypic variation among familial hypercholesterolemics heterozygous for either one of two Afrikaner founder LDL receptor mutations

Two common founder-related gene mutations that affect the low-density lipoprotein receptor (LDLR) are responsible for approximately 80% of familial hypercholesterolemia (FH) in South African Afrikaners. The FH Afrikaner-1 (FH1) mutation (Asp206-->Glu) in exon 4 results in defective receptors with approximately 20% of normal activity, whereas the FH Afrikaner-2 (FH2) mutation (Val408-->Met) in exon 9 completely abolishes LDLR activity (< 2% normal activity). We analyzed the contribution of these mutations and other factors on the variation of hypercholesterolemia and clinical features in Afrikaner FH heterozygotes. The type of FH mutation, plasma triglyceride levels, and age of patients each contributed significantly to the variation in hypercholesterolemia, whereas smoking status, high-density lipoprotein cholesterol levels, and gender had no influence. Although all FH heterozygotes had frank hypercholesterolemia, patients with the FH1 mutation had significantly lower cholesterol levels than those with the FH2 mutation. FH1 heterozygotes also tended to have milder clinical features. The differences between the two FH groups could not be explained by a difference in the common apolipoprotein E variants. This study demonstrates that mutational heterogeneity in the LDLR gene influences the phenotypic expression of heterozygous FH.

XbaI polymorphism of the apolipoprotein B gene and plasma lipid and lipoprotein response to dietary fat and cholesterol: a clinical trial

A dietary trial was carried out on a group of offspring whose parents were hospitalized for an acute myocardial infarction. The XbaI Restriction Fragment Length Polymorphism (RFLP) was used to examine the genetic contribution of variation at this apo B locus to the response of lipids and lipoproteins to dietary manipulations. Twenty participants were homozygotes for the 8.0 kb fragment (X1X1), two were homozygotes for the 5.0 kb fragment (X2X2), and 15 were heterozygotes (X1X2). Subjects were randomized to a 5-week crossover study. Half began on a low SFA--cholesterol (LSC) diet for 5 weeks and, after a washout period of 4 weeks, they were placed on a high SFA--cholesterol (HSC) diet for a second period of 5 weeks. This order was reversed in the second group of participants. Significant changes in total cholesterol, LDL-C, and apo B were observed when subjects were moved from the LSC to the HSF diet. The corresponding average change induced by the dietary manipulations in X1X1 subjects compared with subjects with X2 allele were: 18.1 +/- 17.6 mg/dl and 9.5 +/- 19.6 mg/dl for total cholesterol and 15.8 +/- 15.3 mg/dl and 4.8 +/- 20.9 mg/dl for LDL-C, respectively. Our observation indicated that variation at the apo B XbaI locus may interact with baseline levels to determine individual dietary response in LDL-C level. However, the differences between the genotypic classes were not statistically significant, suggesting that the apo B XbaI locus is not a major determinant of interindividual differences in lipid and lipoprotein response to diet in this population.

Relation of apolipoprotein E phenotype to myocardial infarction and mortality from coronary artery disease

The apolipoprotein E polymorphism is a genetic determinant of low-density lipoprotein (LDL) cholesterol. Its status as a risk factor for coronary artery disease (CAD), either through a causal relation with LDL cholesterol level or independently, is less clearly established. Data from the Multiple Risk Factor Intervention Trial were used to examine the influence of apolipoprotein E phenotype on risk of coronary events. Of the 12,866 randomized participants, 619 were studied in a nested case-control design. CAD deaths (93) and nonfatal myocardial infarctions (113) were matched to 412 controls. The allele frequencies of apolipoprotein E in the white subset (epsilon 2 = 0.06, epsilon 3 = 0.79, and epsilon 4 = 0.15) were very similar to other nonselected white American populations, and the relation of apolipoprotein E on total and LDL cholesterol was generally similar to that seen in other studies, with the epsilon 2 allele being associated with lower and the epsilon 4 allele with higher total and LDL cholesterol. Allele frequencies were not the same for patients and control subjects. The presence of epsilon 4 was associated with an increased risk of CAD that was most evident for fatal cases. There was no relation between changes in LDL cholesterol over time during the trial and apolipoprotein E phenotypes.

Diagnosis of heterozygous familial hypercholesterolemia. DNA analysis complements clinical examination and analysis of serum lipid levels

The concordance of clinical and molecular genetic diagnoses of heterozygous familial hypercholesterolemia (FH) was studied in 65 subjects (10 propositi and 55 first-degree relatives) from 10 families with FH. Nine propositi were carriers of the FH-Helsinki deletion of the low density lipoprotein (LDL) receptor gene, prevalent in the Finnish population, while a new deletion, extending from intron 14 to intron 15 of the LDL receptor gene, was identified in one family. Serum LDL cholesterol levels used in the clinical diagnosis (less than 5.0 mmol/l, not FH; 5.0-5.9 mmol/l, possible FH; greater than or equal to 6.0 mmol/l, FH; limits are 1 mmol/l lower for those less than 18 years) were derived from an authoritative recommendation. Tendon xanthomas constituted an additional criterion. With the DNA analysis as the reference, 55 (85%) subjects could be correctly classified clinically as FH patients or subjects without FH. The remaining 10 subjects were misclassified or were in the "possible FH" category. When the age- and sex-specific 95th percentile LDL cholesterol levels were used instead of the rigid values for both adults and children, the percentage of correct diagnoses rose to 95%. Common genetic polymorphisms of apolipoproteins E and B did not markedly affect LDL cholesterol levels in FH patients, whereas increasing age and obesity were associated with elevated LDL levels. In conclusion, DNA analysis is a valuable adjunct to the diagnosis of FH that is applicable to families with a known mutation of the LDL receptor gene. If DNA methods are not available, age- and sex-specific LDL levels should be used as an aid in the clinical diagnosis of FH.