Apolipoprotein E polymorphism influences lipid phenotypes in Chinese families with familial combined hyperlipidemia.

BACKGROUND: Apolipoprotein E (apoE) polymorphism is associated with changes in the lipoprotein profile of individuals with familial combined hyperlipidemia (FCHL), but its effects on the lipoprotein profiles of members of Chinese families with FCHL remain uncertain. METHODS AND RESULTS: 43 FCHL families (n=449) and 9 normolipidemic families (n=73) were recruited to assess the influence of apoE polymorphism on plasma lipids. The relative frequency of the epsilon4 allele in affected and unaffected FCHL relatives, spouses and normolipidemic members was 13.8%, 5.3%, 9.1% and 6.8%, respectively, with a significantly higher frequency in affected FCHL relatives, compared with unaffected FCHL relatives or normolipidemic members (p=0.0002 or p=0.029). In FCHL relatives, the apoE4 subset (E4/4 and E4/3) exhibited significantly higher levels of apoB, total cholesterol and low-density lipoprotein-cholesterol (LDL-C) than did the apoE3 (E3/3) subset, especially in women (all p<0.05), and there was significant elevation of LDL-C concentrations in men only (p<0.05). In men, the apoE2 (E3/2) subset indicated a decreased level of apoB and increased apoA1 compared with those in the apoE3 subset (p<0.05). Conclusions: ApoE polymorphism appears to be associated with variance of the lipoprotein phenotype in Chinese families with FCHL.     

Plasma homocysteine in subjects with familial combined hyperlipidemia

Familial combined hyperlipidemia (FCH) is characterised by hypercholesterolemia and/or hypertriglyceridemia and associated with an increased risk of cardiovascular disease (CVD). The plasma lipid and lipoprotein levels in subjects with FCH are relatively moderately elevated and do not fully explain the increased risk of CVD. Hyperhomocysteinemia is a disorder of methionine metabolism and also a well-known independent risk factor for CVD. We investigated whether subjects with FCH have higher plasma homocysteine concentrations than controls, and whether homocysteine contributes to the increased risk of CVD in FCH. Furthermore we evaluated whether parameters of lipid and lipoprotein metabolism and/or insulin resistance are associated with the homocysteine level. In total 667 subjects, including 161 subjects with FCH, 109 spouses who referenced as control group and 397 normolipidemic relatives were studied. FCH was defined by the presence of plasma total cholesterol and/or triglyceride levels above the 90th percentile adjusted for age and gender. The mean homocysteine concentration of the FCH group did not significantly differ from the control group. The risk for CVD due to hyperhomocysteinemia in subjects with FCH was not higher than in subjects without FCH. No associations were observed between plasma homocysteine concentration and plasma lipid and lipoprotein levels, including small dense low density lipoprotein, nor between homocysteine concentration and insulin resistance.     

Apolipoprotein B is associated with metabolic syndrome in Chinese families with familial combined hyperlipidemia, familial hypertriglyceridemia and familial hypercholesterolemia

There is a paucity of data concerning the metabolic syndrome (MetS) in families with familial combined hyperlipidemia (FCHL), familial hypertriglyceridemia (FHTG), familial hypercholesterolemia (FH) and normolipidemic families in China. This study investigated the prevalence of MetS in these families and explored potential factors relevant to MetS. We recruited 70 families with 560 individuals > or = 20 years of age, including 43 FCHL families with 379 individuals, 3 FHTG families with 30 individuals, 16 FH families with 102 individuals and 8 normolipidemic families with 49 individuals. The definition of MetS is determined using modified criteria of National Cholesterol Education Program substituting body mass index for waist circumference. MetS is identified in 60.7% of FCHL patients and 71.4% of FHTG patients. The prevalence of MetS in family members is 36.7% for FCHL, 33.3% for FHTG, 17.6% for FH and 16.3% for normolipidemic families, with an odds ratio (OR) of 2.97 (95% CI 1.29-7.07, P=0.007) in FCHL families compared with normolipidemic families. Apolipoprotein B (apoB) is associated with MetS by multiple logistic analysis with an OR of 1.05 (1.03-1.07, P<0.001) in FCHL families, OR of 1.26 (1.03-1.55, P=0.026) in FHTG and OR of 1.07 (1.01-1.12, P=0.014) in FH families, independent of variables including age, gender, apolipoprotein A1, and low density lipoprotein cholesterol. Apolipoprotein A1 provided an OR of 0.95 (0.94-0.97, P<0.001) in FCHL families and OR of 0.94 (0.90-0.97, P=0.011) in FH families, but neither in FHTG nor in normolipidemic families (both P>0.05). Thus, apoB may be regarded as a relevant factor in the assessment of MetS in FCHL, FHTG and FH families. However, this finding needs to be verified by prospective studies in diverse ethnicities and warrants additional studies to elucidate possible mechanisms linking apoB to MetS.     

Effect of fenofibrate on serum lipoproteins in subjects with familial hypercholesterolemia and combined hyperlipidemia

The effects on serum lipoproteins were studied in 8 patients with familial heterozygous hypercholesterolemia and 9 patients with familial combined hyperlipidemia during an 8-week treatment with fenofibrate. VLDL, IDL, LDL and HDL were isolated by ultracentrifugation and precipitation. Lipids and apolipoproteins A-I and B were determined by enzymatic and immunonephelometric techniques, respectively. In hypercholesterolemia, administration of fenofibrate resulted in decreases of VLDL, IDL, and LDL (cholesterol -58.3%, -28.6%, and -24.4%), while, in combined hyperlipidemia, treatment with the drug lowered VLDL and IDL (-33.3% and -42.9%). HDL cholesterol and apolipoprotein A-I increased only in hypercholesterolemia (+22.9% and +6.9%).     

Endothelial dysfunction in a family with familial combined hyperlipidemia

Familial Combined Hyperlipidemia is the most frequent familial hyperlipidemia with a high risk a early manifestation of arteriosclerosis. Endothelial dysfunction is the first step in the development of arteriosclerosis. The aim of our investigation was to examine selected markers of endothelial dysfunction in hyperlipidemic members of families with familial combined hyperlipidemia and their normolipidemia first-line relatives and to compare them with healthy individuals. The study includes non-smoking members of the affected families (probands and first-line relatives), who have not suffered from clinical manifestations of arteriosclerosis and/or hypertension during the start of the study. The cohort was divided into hyperlipidemic individuals (N = 25) and normolipidemic individuals (N = 21). Both groups were compared with control groups of healthy individuals (two groups, N = 17 each), who were adjusted by age and sex. The following markers of endothelial dysfunction were examined: 1. ultrasound--flow mediated dilatation of brachial artery and 2. humoral--serum levels of von Willebrand factor, inhibitor of activator of plasminogen-1 and vasoadhesive molecules (vascular cell adhesion molecule-1, intercellular adhesion molecule-1). The members of families with familial combined hyperlipidemia displayed symptoms of endothelial dysfunction. In comparison with healthy controls the endothelial dysfunction was more expressed in hyperlipidemic individuals. They displayed a significantly lower flow-mediated dilatation of brachial artery (3.6 +/- 3.3% versus 6.6 +/- 2.8%, P < 0.01), higher levels of von Willebrand factor (152.8% +/- 79.1% versus 110.4% +/- 24.8%, P < 0.05), inhibitor of activator of plasminogen-1 (94.6 +/- 30.8 ng/ml versus 60.4 +/- 38.0 ng/ml, P < 0.01) and vasoadhesive molecules: vascular cell adhesion molecule-1 (927.0 +/- 167.7 ng/ml versus 814.7 +/- 171.1 ng/ml, P < 0.05), intercellular adhesion molecule-1 (601.7 +/- 89.5 ng/ml versus 544.8 +/- 59.8 ng/ml, P < 0.05). The normolipidemic individuals displayed only a significantly lower flow-mediated dilatation of brachial artery (5.6 +/- 2.6% versus 7.5 +/- 2.8%, P < 0.05) and higher levels of von Willebrand factor (136.8 +/- 40.32% versus 104.1 +/- 24.9%, P < 0.05). No significant difference was found in the levels of inhibitor of activator of plasminogen-1 and vasoadhesive molecules. The results indicated that members of families with familial combined hyperlipidemia represent a high-risk group from the standpoint of early manifestation of arteriosclerosis.     

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 ε3, ε4, and ε2 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.     

A novel mutation of the apolipoprotein A-I gene in a family with familial combined hyperlipidemia

We report a large family in which four members showed a plasma lipid profile consistent with the clinical diagnosis of familial combined hyperlipidemia (FCHL). One of these patients was found to have markedly reduced HDL cholesterol (HDL-C) (0.72 mmol/l) and Apo A-I (72 mg/dl) levels, a condition suggestive of the presence of a mutation in one of the HDL-related genes. The analysis of APOA1 gene revealed that this patient was heterozygous for a cytosine insertion in exon 3 (c.49–50 ins C), resulting in a frame-shift and premature stop codon at position 26 of pro-Apo A-I (Q17PFsX10). This novel mutation, which prevents the synthesis of Apo A-I, was also found in four family members, including three siblings and the daughter of the proband. Carriers of Apo A-I mutation had significantly lower HDL-C and Apo A-I than non-carriers family members (0.77 ± 0.15 mmol/l vs. 1.15 ± 0.20 mmol/l, P < 0.005; 71.4 ± 9.1 mg/dl vs. 134.0 ± 14.7 mg/dl, P < 0.005, respectively). Two of the APOA1 mutation carriers, who were also heavy smokers, had fibrous plaques in the carotid arteries causing mild stenosis (20%). The intimal-media thickness in the two other adult carriers was within the normal range. The other non-carriers family members with FCHL had either overt vascular disease or carotid atherosclerosis at ultrasound examination. This observation suggests that the low HDL-C/low Apo A-I phenotype may result from a genetic defect directly affecting HDL metabolism, even in the context of a dyslipidemia which, like FCHL, is associated with low plasma HDL-C.     

Two polymorphisms in the apo A-IV gene and familial combined hyperlipidemia

Linkage and association of the apo AI-CIII-IV gene region to familial combined hyperlipidemia (FCHL) was reported previously, based on the presence of genetic variants in the apo CIII and apo AI gene. No data were available yet on the contribution of the apo A-IV locus. Two DNA variants in exon 3 of the apo A-IV gene, A (Thr)(347)T (Ser) and [CTGT](3-4) were characterized by sequencing the coding region of the apo A-IV gene and were analyzed in our Dutch FCHL cohort (30 probands, 159 affected relative, 317 unaffected relatives and 218 spouses). The genotype frequency of the A(347)T variant was different in probands and spouses. In probands no 2/2 carriers were found, resulting in a significant decreased frequency of the 2-allele (P<0.05). This was suggestive for a protective role of the presence of the serine (T) allele on the prevalence of FCHL. No difference in frequency distribution was found for the [CTGT](3-4) variant between the groups. Homozygous 4/4 carriers in spouses had a more favorable lipid profile (LDL-cholesterol and apo B, P<0.05). The absence of linkage disequilibrium of the A(347)T with other markers in the gene cluster, and the absence of linkage disequilibrium with [CTGT](3-4) marker and the MspI-AI marker in the apo A-I promoter showed that these two apo A-IV variants reside on different haplotypes from the apo A-I and apo C-III markers. This was illustrated by extensive haplotype analysis. The present data on the contribution of DNA variants in the apo A-IV gene support our previous observations that the apo AI-CIII-AIV gene cluster has a complex genetic contribution to FCHL both by conferring susceptibility and protection.     

Low density lipoprotein receptor gene mutations in patients with clinical diagnosis of familial hypercholesterolemia.

Low density lipoprotein receptor (LDLR) gene mutations cause familial hypercholesterolemia which is associated with elevated risk of ischemic heart disease. AIM: To define LDLR gene mutations in unrelated patients with heterozygous familial hypercholesterolemia in Russia. METHODS: PCR- single-strand conformation polymorphism analysis, automated DNA sequencing, and test for the presence of the apolipoprotein (apo) B-3500 mutation known to induce hereditary defect in apo-B-100. RESULTS: We found 6 novel mutations of LDLR gene designated E8X, 230insG, 671_679dupGACAAATCT, W422R, D461Y, and V698L. We also identified three missense mutations - C139G, E207K and R395W, which were previously described in FH patients from western populations. None of the studied persons had apo-B-3500 mutation. CONCLUSION: These findings broaden knowledge on mutations responsible for development of familial hypercholesterolemia and confirm molecular heterogeneity of this disease in Russia.     

Relationship of insulin sensitivity and ApoB levels to intra-abdominal fat in subjects with familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is one of the most common familial dyslipidemias associated with premature heart disease. Subjects with FCHL typically have elevated apolipoprotein B (apoB) levels, variable elevations in cholesterol and/or triglycerides, and a predominance of small, dense, low density lipoprotein particles. It is thought that insulin resistance is important in the expression of the combined hyperlipidemia phenotype. To further characterize the relationship between insulin resistance and increased apoB levels, 11 subjects from well-characterized FCHL families and normal control subjects matched for weight and/or age underwent measurement of intra-abdominal fat (IAF) and subcutaneous fat (SQF) by CT scan, insulin sensitivity (Si) by the frequently sampled intravenous glucose tolerance test, and lipoprotein levels. Body mass index and IAF were higher and Si was lower (more insulin resistant) in the FCHL group than in the age-matched group, but the values were similar in the FCHL group and the age- and weight-matched control group. When the relationship between body fat distribution and Si was tested with multiple linear regression, only IAF was significantly correlated with Si after the addition of SQF and body mass index as independent variables. For any level of insulin sensitivity or IAF, however, apoB levels remained higher in the FCHL subjects than in the control groups. In conclusion, in FCHL, visceral obesity is an important determinant of insulin resistance. Visceral obesity and insulin resistance, however, do not fully account for the elevated levels of apoB in this disorder, and this study provides physiological support for separate, but additive, genetic determinants in the etiology of the lipid phenotype.     

Genetics of familial combined hyperlipidemia

Complex disorders are caused by several environmental factors that interact with multiple genes. These diseases are common at the population level and constitute a major health problem in Western societies. Familial combined hyperlipidemia (FCHL) is characterized by elevated levels of serum total cholesterol, triglycerides, or both. This disorder is estimated to be common in Western populations with a prevalence of 1% to 2%. In addition, 14% of patients with premature coronary heart disease (CHD) have FCHL, making this disorder one of the most common genetic dyslipidemias underlying premature CHD. Both genetic and environmental factors are suggested to affect the complex FCHL phenotype, but no specific susceptibility genes to FCHL have been identified. It is hoped that further analysis of the first FCHL locus and other new loci obtained in genome-wide scans will guide us to genes predisposing to this complex disorder.     

The apolipoprotein B R3500Q gene mutation in Spanish subjects with a clinical diagnosis of familial hypercholesterolemia

Familial hypercholesterolemia (FH) and familial defective apolipoprotein B-100 (FDB) are autosomal codominant diseases characterized by elevated LDL cholesterol levels and premature coronary artery disease. Mutations of the LDL-receptor and apolipoprotein B genes, which affect the binding domains of their protein products, are the causal defects. Securing the diagnosis of these conditions by molecular assays is important because it mandates early intervention for coronary risk reduction. DNA screening for apolipoprotein B R3500Q gene mutation was performed in 913 unrelated Spanish individuals with a clinical diagnosis of FH using a modified polymerase chain reaction protocol and restriction enzyme genotyping. Thirteen FDB heterozygotes were identified (frequency of 1.4% in subjects with a clinical diagnosis of FH). The prevalence of hypercholesterolemic subjects with FDB in the general Spanish population was estimated to be as low as 2.8 x 10(-5) (95% CI, -3.1 x 10(-4) to 3.7 x 10(-4)). The ancestors of 11 out of 13 FDB carriers were from Galicia, a region of Celtic ancestry in Northwestern Spain. As the series included 100 unrelated subjects of Galician ancestry, FDB appears to be an important genetic cause of hypercholesterolemia in this region. All the R3500Q mutations were found on the same allele, assigned to haplotype XbaI-/MspI+/EcoRI-/3HVR48, suggesting that the mutant alleles are identical by descent in people from Spain, as observed in other Caucasian populations. In conclusion, the R3500Q mutation of the apolipoprotein B gene, a common cause of FH in central Europe, is infrequent in the general Spanish population, but it is common in Galicia.     

Chylomicron processing in familial dysbetalipoproteinemia and familial combined hyperlipidemia studied with vitamin A and E as markers: a new physiological concept

In previous work we identified a transfer/diffusion process occurring in the postprandial state that more or less contributes to the accumulation of beta-VLDL in familial dysbetalipoproteinemia (FD). Here we present a new theoretical concept underlying chylomicron processing developed on the basis of extended quantitative analyses of fat loading experiments, with both vitamins A and E, performed in patients with familial combined hyperlipidemia (FCH) in comparison to patients with FD and control subjects. Recovery of triglycerides from the fat load in the plasma triglyceride pool was <4%, indicating a very effective lipolysis process with an active remnant generation. Vitamin A from the fat load was, over 48 h, quantitatively recovered in the plasma lipoprotein pool; vitamin E was recovered to 2241%. Nevertheless, transfer/diffusion of both vitamins showed similar patterns. At equilibrium, their contents correlated strongly with the lipoprotein concentrations, the slopes being similar for control subjects and both groups of patients. Only in those FD patients with the highest lipid values, did the vitamin A/lipoprotein mass ratio in the Sf>100 fraction deviate from the total group mean. In the Sf 15-100 fraction, most specific for 'remnants', vitamin A/cholesterol ratios for all subjects were uniform proving that beta-VLDL formation is a thermodynamic process regulated by concentration gradients and the lipophilicity of lipoprotein constituents, not a typical feature for patients with FD. In patients with FD, vitamin A in the plasma pool was recovered excessively (276%) in line with recognition in various pools as a result of the transfer/diffusion process in plasma.     

Lack of agreement between the plasma lipid-based criteria and apoprotein B for the diagnosis of familial combined hyperlipidemia in members of familial combined hyperlipidemia kindreds

Our objective was to analyze the concordance between abnormally high-cholesterol and triglyceride concentrations and increased apoliprotein B (apoB) concentrations for considering subjects as affected in familial combined hyperlipidemia (FCHL) kindreds. Twenty-two FCHL families (n = 217) were included. There was a lack of agreement in the identification of the abnormal subjects when several cholesterol- and triglyceride-based criteria were compared against various apoprotein B-based criteria. The agreement, measured as kappa coefficients, between 14 lipid-based criteria and 8 apoB concentrations is reported. For the most frequently used criterion (> or = 90th percentile for cholesterol or triglyceride concentrations), the agreement was low for all apoB levels (kappa, 0.42 to 0.49). A concentration of triglycerides > or = 150 mg/dL and cholesterol > or = 200 mg/dL was the only criterion with a kappa value above 0.6; the acceptable agreement was found with an apoB concentration > or = 120 mg/dL (kappa = 0.604). In conclusion, the data reported here clearly show that a large degree of diagnostic uncertainty exists in the categorization as normal or abnormal of members of FCHL kindred. Different diagnostic criteria would result in conflicting results. This is a critical issue, depending on the diagnostic criteria used, completely different conclusions could result from the linkage analysis in the FCHL studies.     

Elevated leptin levels in subjects with familial combined hyperlipidemia are associated with the increased risk for CVD

Familial combined hyperlipidemia (FCH) is characterized by hypercholesterolemia and/or hypertriglyceridemia and is associated with premature cardiovascular disease (CVD). Other features of FCH are obesity and insulin resistance. Serum leptin levels have been associated with obesity, insulin resistance and CVD. The aim of this study was to determine whether increased leptin levels contribute to the FCH phenotype and its increased risk for CVD. The study population comprised 644 subjects, including 158 FCH patients. Leptin levels were determined, using a commercially available ELISA. For both males and females, the mean leptin level (ng/ml) was higher in FCH patients compared to normolipidemic relatives and spouses. However, after standardization for BMI and insulin resistance, these differences disappeared. The 90th percentile of the leptin level, standardized for BMI, insulin resistance and gender, was associated with an increased risk for CVD in FCH patients (odds ratio=2.9, 95% CI=1.1-8.0) and in non-FCH subjects (odds ratio=3.4, 95% CI=1.3-9.0). The overall increased risk for CVD, associated with a leptin level >90th percentile, was 3.3 (95% CI=1.7-6.4). We conclude that in patients with FCH, leptin levels are increased in proportion to their higher BMI and the presence of insulin resistance. These increased leptin levels are associated with an increased risk for CVD both in FCH patients and non-FCH subjects, independent of BMI, insulin resistance and gender.     

TXNIP gene not associated with familial combined hyperlipidemia in the NHLBI Family Heart Study

Familial combined hyperlipidemia (FCHL) is the most common familial dyslipidemia, and is implicated in up to 20% of cases of premature coronary heart disease. Positive linkage to chromosome 1q was found in FCHL families participating in the NHLBI Family Heart Study (FHS), replicating linkage found in other studies. The HcB-19 mouse, which shares phenotypes with FCHL, was shown in other studies to have a nonsense mutation in the thioredoxin interacting protein gene (txnip). txnip is a gene on mouse chromosome 3 in a region syntenic with the 1q human FCHL linkage region. We re-sequenced the human homolog of mouse txnip in the FHS sample and identified nine single nucleotide polymorphisms (SNPs). We did not observe the nonsense mutation found in the HcB-19 mouse, and only three of the SNPs discovered were sufficiently polymorphic for analysis. No association between FCHL and the TXNIP gene was found. Within FCHL cases, presence of variants also did not significantly affect body mass index or levels of lipids, insulin, or glucose. Our results suggest that in this sample, TXNIP does not play a major role in FCHL or related traits, and is unlikely to account for the positive evidence of linkage in this region.