Familial defective apolipoprotein B-100: detection in the United Kingdom and Scandinavia, and clinical characteristics of ten cases

Development of apolipoprotein B antisense molecules as a therapy for hyperlipidemia

As new studies demonstrate that lower levels of low-density lipoprotein cholesterol (LDL-C) reduce cardiovascular disease, and as goals for LDL-C in high-risk individuals are reduced further and further, reaching those goals becomes more difficult for a significant percentage of the population. New therapeutic approaches to lower LDL-C would, therefore, be advantageous, particularly in those who are most likely to suffer cardiovascular disease-associated morbidity and mortality. Mouse and human genetic models suggest that decreasing hepatic apolipoprotein B (apoB) production may be a therapeutic approach for the treatment of dyslipidemia. Because antisense oligonucleotides naturally distribute to the liver and can specifically inhibit synthesis of proteins from their messenger RNAs, antisense oligonucleotides represent a potential approach for decreasing the biosynthesis of apoB, and thereby, the production of both very low density lipoprotein (VLDL) and LDL. Newly developed apoB antisense approaches have produced results in animal models and humans, providing proof of concept regarding reductions in LDL-C concentrations. Surprisingly, despite prior experience with inhibitors of microsomal triglyceride transfer protein, which also inhibits the secretion of VLDL, apoB antisense-mediated reduction in VLDL secretion does not appear to cause marked steatosis. The mechanisms whereby two different approaches for inhibiting apoB and triglyceride secretion have different effects on hepatic triglycerides are currently being examined.

Apolipoprotein B levels, APOB alleles, and risk of ischemic cardiovascular disease in the general population, a review

Apolipoprotein B is a key component in lipid metabolism. Subendothelial retention of apolipoprotein B containing lipoproteins is a necessary initiating event in atherogenesis, and high plasma levels of apolipoprotein B is a risk factor for atherosclerosis, whereas low levels may provide protection. The present review examines, with focus on general population studies, apolipoprotein B levels as a predictor of ischemic cardiovascular disease, as well as the association of mutations and polymorphisms in APOB with plasma apolipoprotein B levels, and risk of ischemic cardiovascular disease. The studies can be summarized as follows: (1) apolipoprotein B predicts ischemic cardiovascular events in both genders, and is better than LDL cholesterol in this respect; (2) linkage disequilibrium structure in APOB is more complex than expected from HapMap data, because a minimal set of tag single nucleotide polymorphisms capturing the entire variation in APOB cannot be identified, and thus most polymorphisms must be evaluated separately in association studies; (3) APOB mutations and polymorphisms are associated with a range of apolipoprotein B and LDL cholesterol levels, although the magnitude of effect sizes of common polymorphisms are modest; (4) both mutations and polymorphisms are associated with LDL metabolism in vivo; (5) association of APOB mutations and polymorphisms with lipid and disease phenotype cannot be predicted in silico using evolutionary conservation or existing prediction programs; and finally, (6) except for the E4154K polymorphism that possibly predicts a reduction in risk of ischemic cerebrovascular disease and ischemic stroke, common APOB polymorphisms with modest effect sizes on lipid levels do not predict risk of ischemic heart disease, myocardial infarction, ischemic cerebrovascular disease, or ischemic stroke in the general population.

Familial defective apolipoprotein B-100 in Slovakia: are differences in prevalence of familial defective apolipoprotein B-100 explained by ethnicity?

The objective of this study was to examine frequency of familial defective apo-B-100 (FDB, R3500Q mutation) in probands with the phenotype of familial hypercholesterolemia (FH) and in the general population of 40-year-old subjects in Slovakia and to characterize their lipid and clinical criteria and to compare the frequency of FDB with other populations. We identified 35 patients with FDB among 362 probands with clinical diagnosis of FH and two cases of FDB in the 40-year-old cohort of 2323 subjects from general Slovak population. Probands with FDB differed from those with FH only in plasma triglyceride concentrations (1.84+/-1.4 mmol/l versus 1.45+/-0.98 mmol/l, respectively, p<0.01). Evaluation of personal history of premature atherosclerosis did not show any differences (11.4% in FDB versus 20% in FH, p<0.16). The FDB patients had similar manifestation of xanthomatosis as the FH patients (17.1% versus 8.25%, p<0.25). The frequency of FDB of 9.7% found in the FH patients is among the highest of those reported to date. The frequency of R3500Q mutation of 0.09% found in Slovak 40-year-old subjects did not differ significantly from published population molecular data. Our comparison of estimated FDB frequencies with those which were found by DNA analysis demonstrated that estimated frequencies were not only wider in range, but also significantly higher than those which were assessed by the analysis. The definitive answer to the prevalence of FDB and its biochemical and clinical characteristics requires screening of unbiased samples of the general population from different ethnic groups based on molecular genetic methods.

ApoB-100 R3500Q mutation in the Lebanese population: Prevalence and historical review of the literature

An interesting mutation affecting the Apo-B gene, R3500Q, is known to display variable geographical distribution in the world and is mostly implicated in the pathogenesis of Familial Hypercholesterolemia (FH). The aim of this study is to determine the prevalence of this mutation in the Lebanese population and compare it to the available international literature. DNA from 160 unrelated healthy donors from our HLA-bank was used and the ApoB genotype was determined using the CardioVascular Disease (CVD) StripAssay (this assay is based on a Polymerase Chain Reaction-Reverse Hybridization technique). The R3500Q mutation was not observed in the general Lebanese population. Since the mutation frequency is elevated in Central Europe and tends to decrease as one moves east and south, it disappears completely in the Mediterranean regions such as Spain, Turkey and Israel; therefore, it is rather expected to be absent in Lebanon as well. Our report adds a valuable piece of information regarding this mutation in an Arab country and paves the way for future research involving patients diagnosed with FH in order to assess the role of the R3500Q mutation in the development of this clinical entity.

Mutational analysis in UK patients with a clinical diagnosis of familial hypercholesterolaemia: relationship with plasma lipid traits, heart disease risk and utility in relative tracing

As part of a randomised trial [Genetic Risk Assessment for Familial Hypercholesterolaemia (FH) Trial] of the psychological consequences of DNA-based and non-DNA-based diagnosis of FH, 338 probands with a clinical diagnosis of FH (46% with tendon xanthomas) were recruited. In the DNA-based testing arm (245 probands), using single-strand conformation polymorphism of all exons of the low-density lipoprotein receptor (LDLR) gene, 48 different pathogenic mutations were found in 62 probands (25%), while 7 (2.9%) of the patients had the R3500Q mutation in the apolipoprotein B (APOB) gene. Compared to those with no detected mutation, mean untreated cholesterol levels in those with the APOB mutation were similar, while in those with an LDLR mutation levels were significantly higher (None=9.15+/-1.62 vs LDLR=9.13+/-1.16 vs APOB=10.26+/-2.07 mmol/l p<0.001, respectively). Thirty seven percent of the detected mutations were in exon 3/4 of LDLR, and this group had significantly higher untreated cholesterol than those with other LDLR mutations (11.71+/-2.39 mmol/l vs 9.88+/-2.44 mmol/l, p=0.03), and more evidence of coronary disease compared to those with other LDLR or APOB mutations (36 vs 13% p=0.04). Of the probands with a detected mutation, 54 first-degree relatives were identified, of whom 27 (50%) had a mutation. Of these, 18 had untreated cholesterol above the 95th percentile for their age and gender, but there was overlap with levels in the non-carrier relatives such that 12% of subjects would have been incorrectly diagnosed on lipid levels alone. In the non-DNA-based testing arm (82 probands) only 19 of the 74 relatives identified had untreated cholesterol above the 95th percentile for their age and gender, which was significantly lower (p<0.0005) than the 50% expected for monogenic inheritance. These data confirm the genetic heterogeneity of LDLR mutations in the UK and the deleterious effect of mutations in exon 3 or 4 of LDLR on receptor function, lipids and severity of coronary heart disease. In patients with a clinical diagnosis of FH but no detectable mutation, there is weaker evidence for a monogenic cause compared with relatives of probands with LDLR mutations. This supports the usefulness of DNA testing to confirm diagnosis of FH for the treatment of hyperlipidaemia and for further cascade screening.

A new but frequent mutation of apoB-100—apoB His3543Tyr

ApolipoproteinB 100 (apoB-100) is an important component of atherogenic lipoproteins such as LDL and serves as a ligand for the LDL-receptor. Familial defective apolipoproteinB 100 (FDB) is caused by a R3500Q mutation of the apoB gene and results in decreased binding of LDL to the LDL-receptor. So far FDB is the most frequent and best studied alteration of apoB-100. Apart from this, three other apoB mutations, R3500W, R3531C and R3480W, affecting binding to the LDL-receptor are known to date. We screened the apoB gene segment of codons 3448-3561 by denaturing gradient gel electrophoresis (DGGE) analysis in a total of 853 consecutively sampled German patients undergoing diagnostic coronary angiography for suspected CAD. By this, a new single base mutation was detected and confirmed by DNA sequencing. The mutation, CAC(3543)TAC results in a His3543Tyr substitution in apoB-100 (H3543Y). The prevalence of heterozygotes for H3543Y in the study population was 0.47% compared to 0.12% for the known Arg 3500 Gln (R3500Q) mutation. In conclusion, the new mutation is four times more frequent than "classical" FDB and thus appears to be the most common apoB mutation in Germany.

LDL-receptor mutations in Europe

Familial hypercholesterolemia (FH) is a clinical definition for a remarkable increase of cholesterol serum concentration, presence of xanthomas, and an autosomal dominant trait of either increased serum cholesterol or premature coronary artery disease (CAD). The identification of the low-density lipoprotein (LDL)-receptor (LDLR) as the underlying cause and its genetic characterization in FH patients revealed more insights in the trafficking of LDL, which primarily transports cholesterol to hepatic and peripheral cells. Mutations within LDLR result in hypercholesterolemia and, subsequently, cholesterol deposition in humans to a variable degree. This confirms the pathogenetic role of LDLR and also highlights the existence of additional factors in determining the phenotype. Autosomal dominant FH is caused by LDLR deficiency and defective apolipoprotein B-100 (APOB), respectively. Heterozygosity of the LDLR is relatively common (1:500). Clinical diagnosis is highly important and genetic diagnosis may be helpful, since treatment is usually effective for this otherwise fatal disease. Very recently, mutations in PCSK9 have been also shown to cause autosomal dominant hypercholesterolemia. For autosomal recessive hypercholesterolemia, mutations within the so-called ARH gene encoding a cellular adaptor protein required for LDL transport have been identified. These insights emphasize the crucial importance of LDL metabolism intra- and extracellularly in determining LDL-cholesterol serum concentration. Herein, we focus on the published European LDLR mutation data that reflect its heterogeneity and phenotypic penetrance.

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.

Is there a genetic basis for resistance to atherosclerosis?

Atherosclerosis and its major clinical manifestation, coronary heart disease, is and will remain the main cause of mortality. Reviews on this subject dealt with factors that enhance development of atherosclerosis. This review deals with a new facet, that some individuals are less prone to develop atherosclerosis: (1) despite high cholesterol intake or (2) despite hypercholesterolemia with elevated low-density lipoprotein cholesterol (LDL-C) levels. The variability of response of plasma cholesterol to dietary intake was shown to be regulated by liver x receptor (LXR) that determines the rate of intestinal cholesterol absorption through the ATP-binding cassette (ABC) gene family. Other gene products, such as apolipoprotein-E (apo-E), scavenger receptor-B1 (SR-B1) and acyl coenzyme: cholesterol acyltransferase-2 (ACAT-2) affect cholesterol absorption also. The role of a genetic background for relative resistance to atherosclerosis is highlighted by subjects with familial hypercholesterolemia in whom high plasma cholesterol levels has not curtailed their expected life span. Studies in animals have shown that resistance to atherosclerosis in spite of hypercholesterolemia is affected by factors such as high-density lipoprotein (HDL) phospholipids that enhance reverse cholesterol transport, non-responsiveness to induction or lack of monocyte chemotactic protein-1 (MCP-1), C-C chemokine receptor 2 (CCR2), macrophage colony stimulating factor (MCSF), or vascular cell adhesion molecule-1 (VCAM-1). Since macrophages have been regarded as pro- or anti-atherogenic, evidence was collated that the high activity of scavenger receptors may contribute towards resistance to atherosclerosis if accompanied by adequate amounts of apo-E for cholesterol removal.

Familial defective apolipoprotein B-100 in a group of hypercholesterolaemic patients in Poland. Identification of a new mutation Thr3492Ile in the apolipoprotein B gene

The prevalence of the familial defective apolipoprotein B-100 (FDB) Arg3500Gln mutation in 525 unrelated hypercholesterolaemic Polish subjects was evaluated. DNA samples were screened for FDB mutation using SSCP method. Presence of mutation was confirmed using a mismatch MspI PCR strategy. Plasma lipid levels and clinical characteristics of 13 patients identified as carriers of the mutation and of their 23 affected relatives were analysed and compared with non-affected ones. In the affected individuals a variable expression of lipid concentrations and of atherosclerosis symptoms were observed. The prevalence of FDB Arg3500Gln mutation in hypercholesterolaemic Polish subjects (3.7%) seems to be similar to the frequency reported in other Caucasian hypercholesterolaemic populations. The estimated prevalence of the mutation in general Polish population is relatively high being 1/250. The same haplotype at the apoB locus in the carriers of this mutation in Poland as in other populations from Western Europe suggests its common origin. In one hypercholesterolaemic subject a non-hitherto described mutation was identified. It consisted in C-->T transition in apoB codon 3492 leading to threonine to isoleucine substitution in 3492 position of apoB gene (Thr3492Ile).

Determinants of Variable Response to Statin Treatment in Patients With Refractory Familial Hypercholesterolemia

Abstract —Interindividual variability in low density lipoprotein (LDL) cholesterol (LDL-C) response during treatment with statins is well documented but poorly understood. To investigate potential metabolic and genetic determinants of statin responsiveness, 19 patients with refractory heterozygous familial hypercholesterolemia were sequentially treated with placebo, atorvastatin (10 mg/d), bile acid sequestrant, and the 2 combined, each for 4 weeks. Levels of LDL-C, mevalonic acid (MVA), 7-α-OH-4-cholesten-3-one, and leukocyte LDL receptor and hydroxymethylglutaryl coenzyme A reductase mRNA were determined after each treatment period. Atorvastatin (10 mg/d) reduced LDL-C by an overall mean of 32.5%. Above-average responders (ΔLDL-C −39.5%) had higher basal MVA levels (34.4±6.1 μmol/L) than did below-average responders (ΔLDL-C −23.6%, P <0.02; basal MVA 26.3±6.1 μmol/L, P <0.01). Fewer good responders compared with the poor responders had an apolipoprotein E4 allele (3 of 11 versus 6 of 8, respectively; P <0.05). There were no baseline differences between them in 7-α-OH-4-cholesten-3-one, hydroxymethylglutaryl coenzyme A reductase mRNA, or LDL receptor mRNA, but the latter increased in the good responders on combination therapy ( P <0.05). Severe mutations were not more common in poor than in good responders. We conclude that poor responders to statins have a low basal rate of cholesterol synthesis that may be secondary to a genetically determined increase in cholesterol absorption, possibly mediated by apolipoprotein E4. If so, statin responsiveness could be enhanced by reducing dietary cholesterol intake or inhibiting absorption.

The molecular mechanism for the genetic disorder familial defective apolipoprotein B100

Familial defective apolipoprotein B100 (FDB) is a genetic disorder in which low density lipoproteins (LDL) bind defectively to the LDL receptor, resulting in hypercholesterolemia and premature atherosclerosis. FDB is caused by a mutation (R3500Q) that changes the conformation of apolipoprotein (apo) B100 near the receptor-binding site. We previously showed that arginine, not simply a positive charge, at residue 3500 is essential for normal receptor binding and that the carboxyl terminus of apoB100 is necessary for mutations affecting arginine 3500 to disrupt LDL receptor binding. Thus, normal receptor binding involves an interaction between arginine 3500 and tryptophan 4369 in the carboxyl tail of apoB100. W4369Y LDL and R3500Q LDL isolated from transgenic mice had identically defective LDL binding and a higher affinity for the monoclonal antibody MB47, which has an epitope flanking residue 3500. We conclude that arginine 3500 interacts with tryptophan 4369 and facilitates the conformation of apoB100 required for normal receptor binding of LDL. From our findings, we developed a model that explains how the carboxyl terminus of apoB100 interacts with the backbone of apoB100 that enwraps the LDL particle. Our model also explains how all known ligand-defective mutations in apoB100, including a newly discovered R3480W mutation in apoB100, cause defective receptor binding.

Apolipoprotein B gene polymorphisms: prevalence and impact on serum lipid concentrations in hypercholesterolemic individuals from Brazil

Genetic polymorphisms at the apolipoprotein B (apo B) have been associated with elevated plasma concentrations of low-density lipoprotein (LDL) cholesterol, atherosclerosis and increased risk for coronary artery disease (CAD). In the present study, four apo B gene polymorphisms (MspI, XbaI, Ins/Del and 3'HVR) have been investigated to determine their frequencies and influence on the lipid profile of 177 hypercholesterolemic white Brazilian subjects (HG) and 100 control individuals (CG). The genotype distribution and allele frequency of MspI, XbaI and Ins/Del polymorphisms of apo B gene were similar between HG and CG groups. The frequency of the alleles smaller than 43 repeats (< or =43) of 3'HVR polymorphism in the HG group was higher when compared to controls (16.4 vs. 8.5%, P<0.05). Moreover, these alleles were associated with higher total cholesterol concentrations in serum of hypercholesterolemic individuals (P<0.05). In addition, an association between Ins/Del and 3'HVR polymorphism was observed. The alleles < or =43 and Del were more frequent in the HG when compared to the CG individuals (P<0.05). We concluded that 3'HVR polymorphism at the apo B gene may be an important genetic marker to evaluate atherosclerotic disease risk.

Familial defective apolipoprotein B-100: detection and haplotype analysis of the Arg(3500)-->Gln mutation in hyperlipidemic Chinese

Familial defective apolipoprotein (apo) B-100 (FDB) is caused by R3500Q mutation of the apo B gene resulting in decreased binding of LDL to the LDL receptor. Two other apo B mutations, R3500W and R3531C, affecting binding are known to date. We screened the apo B gene segment around codon 3500 by heteroduplex analysis and single strand conformation polymorphism (SSCP) analysis in a total of 373 hyperlipidemic individuals. Two single-base mutations were detected and confirmed by DNA sequencing. One mutation, ACA(3528)-->ACG change, resulted in degenerate codon with no amino acid substitution. The other mutation, CGG(3500)-->CAG mutation, resulted in an Arg(3500)-->Gln substitution (R3500Q). The prevalence of heterozygote in this selected population was 0.3% (95% confidence interval, 0.01-1.5%) for the R3500Q mutation, and 2.4% (95% confidence interval, 1.1-4.5%) for the previously described R3500W mutation. The results suggest that the R3500Q mutation is not a significant factor contributing to moderate hypercholesterolemia in Chinese (P=0.027). Family studies of the R3500Q carrier revealed a further two individuals heterozygous for the mutation, both of whom were hypercholesterolemic. Analysis of the R3500Q allele using six diallelic markers and the 3'HVR marker revealed a haplotype which was the same as that reported in a Chinese American but differed from that reported in a Chinese Canadian. Our data support limited multiple recurrent origins for R3500Q in Chinese population.

Flow Cytometric Assessment of LDL Ligand Function for Detection of Heterozygous Familial Defective Apolipoprotein B-100

Background: Familial defective apolipoprotein (apo) B-100 (FDB) is caused by a mutation in the apoB gene and characterized by decreased binding of LDL to LDL receptors because of reduced function of the apoB-100 ligand. FDB may be associated with severe hypercholesterolemia and cannot always be distinguished from familial hypercholesterolemia phenotypically.

Methods: We used a fluorescence flow cytometry assay with Epstein-Barr virus-transformed lymphocytes to detect reduced LDL ligand function by competitive binding with fluorescently conjugated LDL (DiI-LDL). The assay was tested and validated using LDL from patients heterozygous for the Arg3500-Gln mutation and their first-degree relatives. Knowing the actual apoB genotype of patients and relatives allowed us to assess the ability of the assay to predict the results of DNA analysis. The results were compared to measurements of LDL ligand function in unrelated healthy control subjects to characterize functionally the Arg3500-Gln mutation.

Results: Fluorescence was significantly increased in cells incubated with DiI-LDL in competition with unlabeled LDL from FDBR3500Q heterozygotes compared with cells incubated with DiI-LDL in competition with unlabeled LDL from relatives or unrelated healthy control subjects. Thus, patients heterozygous for the Arg3500-Gln mutation had significantly reduced LDL ligand function. The binding affinity of LDL from FDBR3500Q heterozygotes was 32% of that in non-FDB relatives and healthy controls. The assay had a diagnostic sensitivity of 0.95 and diagnostic specificity of 0.89.

Conclusions: The diagnostic accuracy of the assay was too low to allow reliable diagnosis of individual cases of heterozygous FDBR3500Q. However, fluorescence flow cytometry may supplement genetic identification of FDB and functionally characterize gene mutations associated with major reductions in LDL ligand function.

Variation of apolipoprotein B as a possible cause of decreased low density lipoprotein clearance and hypercholesterolemia

The fractional catabolic rate (FCR) for low density lipoprotein (LDL) apolipoprotein B (apo B) was studied to explore the variations in apo B as a possible cause of hypercholesterolemia. The FCR of radioiodine labelled autologous LDL and homologous LDL isolated from a normocholesterolemic subject were compared in forty-nine type II hypercholesterolemic males and females with the mean plasma concentration of total cholesterol of 7.78 mmol/l, LDL-cholesterol 5.41 mmol/l and triglycerides 2.09 mmol/l. In most patients the autologous LDL was catabolized at an equal rate and sometimes even faster than the homologous LDL. However, twelve out of forty-nine patients catabolized homologous LDL 0.8-19.3% faster than autologous LDL and several apo B polymorphisms were determined. No apo B-3500 or apo B-3531 mutations were detected. Patients with XbaI -/- (absence of cutting site) had lower total, IDL and LDL cholesterol and LDL apoB than the other genotypes. Patients with EcoRI +/+ (presence of cutting site) had higher total, VLDL and LDL cholesterol and slower FCR for autologous LDL, and their VLDL was richer in cholesterol than that of patients with the EcoRI +/-. The MspI and ins/del polymorphisms were not associated with variations in the measured parameters. The apo E 4 was associated with higher VLDL and IDL cholesterol, higher triglycerides and LDL apo B than E 3/3. Overall, the determined apo B polymorphisms were not related to the slow clearance of autologous LDL among the 12 patients, in whom autologous LDL was cleared at a slower rate than homologous LDL. In conclusion, hypercholesterolemia can be due to particle-related slow clearance of LDL in some patients. However, this is not a common cause of hypercholesterolemia.

The type of mutation in the low density lipoprotein receptor gene influences the cholesterol-lowering response of the HMG-CoA reductase inhibitor simvastatin in patients with heterozygous familial hypercholesterolaemia

In a genetically heterogeneous group of 109 patients with a clinical diagnosis of heterozygous familial hypercholesterolaemia (FH), the influence of gender, apolipoprotein (apo) E genotype and the type of molecular defect in the LDL-receptor (LDLR) gene on the reduction of plasma LDL-cholesterol levels to treatment with a HMG-CoA reductase inhibitor (simvastatin) were studied. Response was determined as the percentage fall in LDL-cholesterol from untreated levels and as the proportion of patients where levels fell below 4.9 or 4.1 mmol/l. Of the patients, 86 individuals had tendon xanthomata (TX+) and a diagnosis of 'definite' FH and these individuals presented with a significantly higher untreated LDL-cholesterol compared to the 23 individuals who did not have xanthomas (TX-) and a diagnosis of 'probable' FH (8.14+/-0.19 vs. 6.81+/-0.25, P= 0.001). Overall, HMG-CoA reductase inhibitor doses of 10, 20 or 40 mg/day resulted in a significant fall of LDL-cholesterol levels of 29, 39 and 49%, but at all doses those with TX had significantly higher levels than those without, and significantly fewer TX + patients achieved LDL-cholesterol levels below 4.9 or 4.1 mmol/l than the TX - group (P < 0.05 at each dose). In the TX+ group the response to treatment was of similar magnitude in men and women and in patients with different apoE genotype. In the 'probable' FH probands only three mutations were identified (detection rate 13%), one in the LDLR gene and two in the APOB gene, a detection rate significantly lower (P= 0.02) than in the 'definite' FH probands where 28 mutations were detected (detection rate 37%). In the TX + patients where no mutation was detected, treatment resulted in a greater proportion achieving LDL-cholesterol levels below 4.9 and 4.1 mmol/l compared to those with any LDLR mutation, this difference was close to statistical significance at the 4.9 mmol/l threshold at 10 mg/day (41 vs. 13%, P = 0.058). For the 14 patients with an LDLR mutation that was predicted to be 'severe', fewer achieved LDL-cholesterol levels below 4.9 or 4.1 mmol/l at each dosage compared to the 16 individuals with 'mild' mutations, and this difference was statistically significant at the maximal dosage of 40 mg/day (P = 0.018). Thus although characterisation of the molecular defect in FH patients may not be relevant to their immediate clinical management, those with a particular mutation may need more aggressive lipid-lowering treatment to reach LDL-cholesterol levels recommended to reduce the risk of coronary heart disease (CHD).

Identification and haplotype analysis of apolipoprotein B-100 Arg3500→Trp mutation in hyperlipidemic Chinese

DNA screening for apolipoprotein (apo) B-100 mutations was performed in hyperlipidemic Chinese. The apo B-100 gene segment surrounding previously identified familial defective apo B-100 (FDB) mutations was amplified by PCR and subjected to single-strand conformation polymorphism (SSCP) analysis. One subject’s aberrant SSCP band was cloned and sequenced to study the molecular lesions. A recurrent ArgCGG-to-TrpTGG mutation (R3500W) in the codon 3500 of the apo B-100 gene was identified. The C-to-T transition creates a NlaIII site and permits rapid restriction analysis of the mutation. A total of 373 hyperlipidemic patients and 309 controls were screened for R3500W. Nine unrelated subjects were shown to be heterozygous for the mutation, and no R3500W carriers were found in the control group (P = 0.004). Six polymorphic markers, including five restriction fragment length polymorphisms and one hypervariable repeat region, were used for haplotype analysis on the mutant allele. In two families, the R3500W mutation could be unambiguously assigned to a unique haplotype XbaI−/MaeI+/MspI+/EcoRI+/Eco57I+/34 3′HVR repeats; in the other seven unrelated heterozygotes, this finding was consistent when an unequivocal haplotype was deduced. The results suggest that all R3500W alleles are identical by descent in our population. The fact that the same mutant allele was identified in other Asians with FDB indicates a common Asian origin for the R3500W mutations.

Estimation of the age of the ancestral arginine3500-->glutamine mutation in human apoB-100

Familial defective apoB-100 (R3500Q) [FDB (R3500Q)] is caused by a mutation in the apoB gene (2p23.24). Almost all individuals with this disorder are of European descent, and in almost all cases the mutation is on a chromosome with a rare haplotype (194) at the apoB locus, suggesting that all FDB (R3500Q) probands are descended from a common ancestor in whom the original mutation occurred. The distribution of the mutation is consistent with an origin in Europe 6000-7000 years ago. We have estimated the amount of recombination between the apoB gene and markers on chromosome 2 in 34 FDB (R3500Q) probands in whom the mutation is on a 194 haplotype. Significant linkage disequilibrium was found between the apoB gene and marker D2S220. We have identified three YACs that contain the apoB gene and D2S220. The shortest restriction fragment common to the three YACs that contained both loci was 240 kb long. No shorter fragments with both loci were identified. On the assumption that 1000 kb corresponds to 1 cM, we deduce that the recombination distance between D2S220 and the apoB gene is about 0.24 cM. Combining this value with the linkage disequilibrium observed between the two loci in the probands, we estimate that the ancestral mutation occurred about 270 generations ago. We postulate that the original mutation occurred in the common ancestor of living FDB (R3500Q) probands, who lived in Europe about 6750 years ago. The errors in this estimate are discussed.

Detecting familial defective apolipoprotein B-100: three molecular scanning methods compared

Familial defective apolipoprotein (apo) B-100 (FDB), a condition that may give rise to hypercholesterolemia, is caused by mutations around codon 3500 of the apo B gene. We have compared the ability of three molecular-scanning techniques, heteroduplex analysis, single-strand conformation polymorphism (SSCP) analysis, and denaturing gradient gel electrophoresis (DGGE), to detect these mutations in a cohort of 432 hypercholesterolemic individuals. Heteroduplex analysis and DGGE detected 11 individuals with apo B mutations, 9 of whom were heterozygous for apo B R3500Q and 2 who were heterozygous for apo B R3531C. Whereas DGGE was able to distinguish between these two mutations, heteroduplex analysis was technically simpler and gave a higher sample throughput. In contrast, SSCP analysis detected only 7 of the R3500Q and none of the R3531C heterozygotes and was the most complex of the three techniques. We believe heteroduplex analysis to be the method of choice for screening large numbers of samples for FDB.

Differences in the phenotype between children with familial defective apolipoprotein B-100 and familial hypercholesterolemia

Familial defective apolipoprotein B-100 (FDB) is a dominantly inherited genetic disorder resulting from a point mutation in the apolipoprotein (apo) B gene and is associated with significantly elevated plasma total and LDL cholesterol levels. Despite numerous descriptions outlining the phenotype of children with familial hypercholesterolemia (FH), no study has described the biochemical and clinical phenotype in a cohort of children with FDB. The phenotypes of FH and FDB, therefore, have not been compared in children. We have studied a cohort of 38 Dutch children (all <20 years old) with FDB from 21 different families. Lipid and lipoprotein levels and the clinical phenotype were compared with 97 age-matched FH heterozygotes, as defined by molecular analysis, and with age-matched non-FDB, non-FH control subjects. Female FDB carriers (n=23) had significantly lower total cholesterol (P<.001), LDL cholesterol (P=.001), total cholesterol:HDL ratio (P<.001), and apoB levels (P=.001) than age-matched female FH heterozygotes (n=50). Similar results were noted in male FDB carriers (n=15) compared with male FH heterozygotes (n=47; P=.005, P=.007, P=.014, and P=.074, respectively). Within the FDB group, female FDB heterozygotes had higher LDL cholesterol (P=.038) and a trend to higher total cholesterol levels (P=.165) than age-matched males. Both male and female FDB carriers had significantly higher total cholesterol, LDL cholesterol, and total cholesterol:HDL ratio than age- and sex-matched control subjects, which was evident even in children <10 years of age, providing additional evidence that this mutation is penetrant in early life. These results provide evidence for a milder biochemical phenotype in children with FDB than in children with FH. The phenotype observed is intermediate between that of control subjects and FH heterozygotes matched for age and sex. As the incidence of coronary artery disease is related to both the extent and duration of cholesterol elevation, our findings might explain in part the lower incidence of clinical atherosclerosis seen in adults with this condition than in adults with FH.

Phenotypic variation in patients heterozygous for familial defective apolipoprotein B (FDB) in three European countries

A glutamine-for-arginine substitution at amino acid position 3500 of apolipoprotein B (apo B) causes synthesis of LDL with reduced binding affinity to the LDL receptor (LDLR). The associated clinical syndrome has been named familial defective apolipoprotein B- 100 (FDB). In 205 FDB patients from Germany (n = 73). The Netherlands (n = 87), and Denmark (n = 45), we tried to assess determinants of variation in lipid concentrations. Besides age, sex, and geographic origin, variation in the LDLR gene was the most powerful determinant of variation in total cholesterol and LDL cholesterol levels. Polymorphic variation in the LDLR gene (SfaNI, exon 2; Nco I, exon 18) was associated with total cholesterol (TC) and LDL cholesterol (LDL-C) variation in women (SfaNI: P = .04 and .03 for TC and LDL-C, respectively; Nco I; P = .003 and .006, respectively), whereas the Ava II (exon 13) and the Pvu II (intron 15) polymorphisms were not. Combined information from all three LDLR exon polymorphisms showed that subjects with at least one S + A + N + allele had 13% to 20% higher TC than non-S + A + N + subjects (P = .02 [TC, men]; P = .01 [LDL-C, men]; P = .005 [TC, women]; and P = .004 [LDL-C, women]) and, together with age and geographic origin, accounted for 20% (women) and 19% (men) of the variation in LDL-C. The expected association of the apo E genotypes (e3e2, e3e3, and e3e4) with cholesterol concentrations was seen in S + A + N + but not in non-S + A + N + subjects and in P-P- but not in P + P + or P + P- subjects. With regard to clinical expression, FDB patients had lower TC and LDL-C levels and a lower prevalence of cardiovascular disease than 101 Danish patients with familial hypercholesterolemia.

Familial ligand-defective apolipoprotein B-100: detection, biochemical features and haplotype analysis of the R3531C mutation in the UK

Familial ligand-defective apolipoprotein (apo) B-100 (FDB) is an autosomal codominant disorder which may give rise to hypercholesterolaemia. It is caused by the substitution of glutamine for arginine at codon 3500 of the apo B gene (apo B R3500Q), resulting in decreased binding of low density lipoprotein (LDL) to the LDL receptor. In order to search for other mutations in this region of the apo B gene, we have screened genomic DNA, obtained from 412 hypercholesterolaemic individuals, using heteroduplex analysis. Additional heteroduplex bands were observed following analysis of DNA from 11 individuals, nine of whom were heterozygous for apo B R3500Q. The two remaining individuals, both of Celtic origin, were shown by DNA sequencing to be heterozygous for a C-->T transition at nucleotide 10800 of the apo B gene, resulting in the substitution of cysteine for arginine at codon 3531 (apo B R3531C). Both had a strong family history of atherosclerosis and family studies revealed a further four individuals heterozygous for the mutation, three of whom were hypercholesterolaemic. Individuals heterozygous for apo B R3531C and R3500Q had mean +/- S.E.M. cholesterol concentrations of 7.82 +/- 0.68 and 8.53 +/- 0.31 mmol/l, respectively. These values were significantly higher than the value of 5.51 +/- 0.23 mmol/l observed in their unaffected relatives. These findings suggest that apo B R3531C is both less common in the UK and gives rise to a less severe form of hypercholesterolaemia than the classical 3500 mutation. In one of the families, the R3531C mutation occurred on a haplotype, compatible with that previously assigned to the mutation in a North American family also of Celtic origin. This is consistent with the mutation having been inherited from a common distant ancestor in individuals of Celtic origin.

Detection and characterization of a novel splice mutation in the LDL receptor intron 12 resulting in two different mutant mRNA variants

Using a simple, standardized denaturing gradient gel electrophoresis (DGGE) based mutation screening technique, a novel G-to-A mutation in the last base of the intron 12 splice acceptor site of the LDL receptor gene was found in 2 Danish families with familial hypercholesterolemia (FH). The mutation is shown to result in 2 mRNA splice variants, both leading to truncated LDLR proteins, containing only the first 594 of the normal 839 amino acids. In one of the FH-families harbouring the mutation, a striking difference in the clinical picture amongst biochemically diagnosed FH patients was clarified when genetic analysis showed that 2 hypercholesterolemic family members, who despite advanced age had no atherosclerotic disease, had not inherited the family LDLR mutation. DGGE analyses of the LDLR exons, LDLR promoter, and apolipoprotein B codon 3456-3553 as well as Southern blotting of the LDLR gene were without signs of other mutations in the non-atherosclerotic hypercholesterolemics of the family. Availability of the clinically applicable mutation screening assay for FH may thus aid in defining reasons for phenotypic differences in FH families and potentially supply information allowing a more differentiated therapeutic approach to individual members of FH families.

Familial defective apolipoprotein B-100: a study of patients from lipid clinics in Scotland and Wales

Familial defective apolipoprotein (apo) B-100 (FDB) is an autosomal codominant disorder, which may be associated with hypercholesterolaemia. The defect is caused by the substitution of glutamine for arginine at amino acid residue 3500 of apo B-100. A total of 357 hypercholesterolaemic patients, 48 with a clinical diagnosis of familial hypercholesterolaemia attending lipid clinics in Scotland and Wales, were screened for the presence of FDB. Seven unrelated individuals, five of whom had a family history of coronary heart disease, and a further 11 first-degree relatives, were shown to be heterozygous for the mutation. Pedigree analysis demonstrated the mutation to be present on a single haplotype, suggesting that in Britain it is inherited from a common ancestor. Treatment of 11 heterozygous individuals with lipid-lowering medication showed falls in total and low density lipoprotein cholesterol ranging from 11.6 to 38.8% and 5.3 to 49.5%, respectively. In view of the condition's association with coronary heart disease and hypercholester-olaemia, it may be worthwhile identifying carriers attending lipid clinics, so that affected siblings can be offered cholesterol-lowering treatment where necessary.

Genetic diagnosis of familial hypercholesterolemia in affected relatives using pedigree tracing

OBJECTIVES

To describe a process of diagnosing familial hypercholesterolemia (FH) at the DNA level in selected family members of affected individuals.

DESIGN AND METHODS

A 63-year-old male patient presented with cholesterol elevations consistent with heterozygous familial hypercholesterolemia. Through participation with the international "MEDPED FH" project to detect affected relatives and to identify their LDL-receptor mutation, the patient was discovered to carry the Lebanese mutation, whereby the codon for cysteine at residue 660 instead codes for a premature termination (C660X), thus truncating the protein product. This mutation also created a new restriction recognition site for the endonuclease Hinfl, which permitted rapid detection of the mutation in selected family members using restriction fragment-length polymorphisms.

RESULTS

The patient's son, who had cholesterol levels consistent with heterozygous FH, was also found to be a heterozygote for the C660X variant of the LDL-receptor.

CONCLUSIONS

Diagnosis of familial hypercholesterolemia at the DNA level is possible as a relatively rapid screening technique in families with a known LDL-receptor mutation, established through participation with the MED-PED FH project.

Plasma mevalonic acid, an index of cholesterol synthesis in vivo, and responsiveness to HMG-CoA reductase inhibitors in familial hypercholesterolaemia

Fasting plasma mevalonic acid (MVA), an indicator of in vivo cholesterol synthesis, was measured in 35 patients with familial hypercholesterolaemia (FH) of whom 7 were treated with pravastatin 10-40 mg/day, 7 with simvastatin 10-40 mg/day and 21 with atorvastatin 80 mg/day. Reductions in low density lipoprotein (LDL) cholesterol and MVA on maximal dose therapy differed significantly between the three drugs: 34.7%, 42.9% and 54.0% (P = 0.0001), and 31.6%, 48.9% and 58.8% (P = 0.004), respectively. Patients on atorvastatin were subdivided according to whether their reduction in LDL cholesterol on treatment was above or below the mean percentage change for the whole group. Basal values of LDL cholesterol did not differ significantly, but above average responders had a significantly higher mean pre-treatment level of MVA (6.2 +/- 0.60 vs. 4.3 +/- 0.61 ng/ml, P < 0.05) than below average responders. When all three drug groups were pooled above average responders showed a significantly greater absolute decrease in MVA on treatment than below average responders (3.85 +/- 0.48 vs. 2.33 +/- 0.40 ng/ml, P < 0.05). However, there was no significant correlation between the magnitude of the decreases in LDL cholesterol and MVA. These findings suggest that FH patients who responded well to statins had a higher basal level of plasma MVA, i.e. a higher rate of cholesterol synthesis, which was more susceptible to pharmacological inhibition. The more marked cholesterol lowering effect of atorvastatin 80 mg/day presumably reflects, at least in part, its ability to inhibit HMG-CoA reductase to a greater extent than maximal recommended doses of pravastatin and simvastatin of 40 mg/day.

Plasma cholesterol esterase level is a determinant for an atherogenic lipoprotein profile in normolipidemic human subjects

Plasma cholesterol level is controlled by various factors. In the present study, high plasma activity of cholesterol esterase was found to correlate with plasma total cholesterol and low density lipoprotein (LDL) cholesterol levels in normolipidemic human subjects. However, the cholesterol esterase is not elevated in plasma of patients with familial hypercholesterolemia. These observations suggest that cholesterol esterase level is not determined by plasma cholesterol level, but elevated cholesterol esterase may be causative in increasing plasma cholesterol and LDL. Additional experiments further demonstrated that cholesterol esterase can convert the larger and less-atherogenic LDL to the smaller and more atherogenic LDL subspecies in vitro. These results suggest that plasma cholesterol esterase contributes to the formation and accumulation of atherogenic lipoproteins, and thus is a major risk factor for premature atherosclerosis in normal human subjects.

The genetic determinants of plasma cholesterol and response to diet

In general, risk factors for multifactorial disorders such as atherosclerosis and hyperlipidaemia show a continuous distribution in the population, and this is the result of both interaction between genetic variation at genetic loci, and genetic and environmental interaction. Therefore, the investigation of the genetics of intermediate phenotypes such as levels of plasma lipid traits is likely to be particularly informative. Once the genes involved in determining the levels of these phenotypes have been identified, it should be possible to use the information to obtain a better understanding of the way these genetic variations determine the clinical end points. In the population it will be possible to identify a number of polygenes that are having a small effect on determining the trait, but for a particular individual, or the relatives of that individual, only a subset of all these polygenes will determine the level of the trait and therefore the risk of developing the disorder. In general, mutations with a large effect on the trait are rare in the population, By contrast, polymorphisms with a small effect on the trait may be common, such as is found with the effect of the apoE alleles and variation at the apoB gene locus on lipid levels. In the field of hyperlipidaemia and atherosclerosis research, molecular techniques have already given a great deal of information on how specific sequence variations in some of the candidate genes are involved in determining levels of plasma apoproteins, lipoproteins and lipids. As more mutations and sequence variations are identified, this will not only aid our understanding of the underlying pathology, but should be useful for identifying individuals who are at risk of developing atherosclerosis because of their particular genotype or combination of genotypes.

Patients with apoE3 deficiency (E2/2, E3/2, and E4/2) who manifest with hyperlipidemia have increased frequency of an Asn 291-->Ser mutation in the human LPL gene

Approximately 1% to 2% of persons in the general population are homozygous for a lipoprotein receptor-binding defective form of apoE (apoE2/2). However, only a small percentage (2% to 5%) of all apoE2/2 homozygotes develop type III hyperlipoproteinemia. Interaction with other genetic and environmental factors are required for the expression of this lipid abnormality. We sought to investigate the possible role of LPL gene mutations in the development of hyperlipoproteinemia in apoE2/2 homozygotes and in apoE2 heterozygotes. As a first step, we performed DNA sequence analysis of all 10 LPL coding exons in 2 patients with the apoE2/2 genotype who had type III hyperlipoproteinemia and identified a single missense mutation (Asn 291-->Ser) in exon 6 of the LPL gene. The mutation was then found in 5 of 18 patients with type III hyperlipoproteinemia who had the apoE2/2 genotype (allele frequency = 13.9%; P < or = 7.4 x 10(-5)) and 6 of 22 hyperlipidemic E2 heterozygous patients with the apoE3/2 and E4/2 genotype (allele frequency = 13.6%; P = 2.2 x 10(-5)). In contrast, this mutation was found in only 3 of 230 normolipidemic controls (allele frequency = 0.7%). In vitro mutagenesis studies revealed that the Asn 291-->Ser mutant LPL had approximately 60% of LPL catalytic activity and approximately 70% of specific activity compared with wild-type LPL. The heparin-binding affinity of the mutant LPL was not impaired. Our data suggest that the Asn 291-->Ser substitution is likely to be a significant predisposing factor contributing to the expression of different forms of hyperlipidemia when associated with other genetic factors such as the presence of apoE2.

Differences in the phenotypic characteristics of subjects with familial defective apolipoprotein B-100 and familial hypercholesterolemia

Familial defective apolipoprotein B-100 (FDB) is a recently identified autosomal-dominantly inherited disorder caused by a point mutation in the apolipoprotein (apo) B gene. To determine whether the phenotypic characteristics in FDB subjects are similar to those in subjects with familial hypercholesterolemia (FH), 76 kindreds fulfilling the clinical criteria for heterozygous FH/FDB were characterized using molecular biological techniques. Allele-specific polymerase chain reaction (PCR) at the apoB locus was used for diagnosis or exclusion of FDB. PCR-based methods for detection of two point mutations (V408M and P664L) at the LDL receptor (LDLR) locus, cosegregation analysis using eight restriction fragment length polymorphisms (RFLPs) at the LDLR locus, or the exclusion of FDB confirmed the clinical diagnosis of FH. Three kindreds were not included because of a missing cosegregation between a particular haplotype and the FH phenotype. We predicted that a similar number of kindreds would be detected in the two groups, assuming comparable prevalences of the diseases in our population and similar phenotypic characteristics. However, only nine kindreds were identified with the FDB mutation compared with 64 kindreds with FH (P < .0001). From these 73 kindreds, 28 FDB heterozygotes and 129 FH heterozygotes were compared using multivariate analysis. There were no differences between these two groups with respect to age, sex, and apoE genotype distribution, lipoprotein(a) concentrations, body mass index, blood pressure, and smoking habits. However, FDB subjects demonstrated significantly lower concentrations of total cholesterol (8.1 versus 10.2 mmol/L, P < .001), LDL cholesterol (6.3 versus 8.2 mmol/L, P < .001), and triglycerides (1.3 versus 1.8 mmol/L, P = .025) and higher concentrations of HDL cholesterol (1.4 versus 1.2 mmol/L, P = .015) than subjects with FH. In contrast to FH, female FDB subjects tended to have higher concentrations of total cholesterol (8.9 versus 7.5 mmol/L, P = .032) and LDL cholesterol (7.1 versus 5.7 mmol/L, P = .026) than FDB males. The same results regarding total and LDL cholesterol and sex differences were observed when individual data of 238 FDB and 415 FH subjects from the literature were compared. In addition, FDB subjects showed much larger total cholesterol fluctuations than FH subjects (median of intraindividual coefficients of variation: FDB, 14.5%; FH, 5.3%; P < .001). In summary, these results demonstrate that FDB subjects tend to have a milder form of hyperlipoproteinemia than FH subjects and that only a part of the subjects with FDB fulfill the established criteria for identifying FH.

Cellular processing of apolipoprotein B-containing lipoproteins from young post-infarction patients and healthy controls

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity was measured in fibroblasts incubated with large (Sf > 60) and small (Sf 20-60) very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) particles, at similar protein concentrations, from young post-infarction patients and healthy controls. The results showed that apolipoprotein (apo) B-containing lipoproteins (VLDL, IDL, LDL) from patients suppressed HMG-CoA reductase activity to a similar extent compared to apo B-containing lipoproteins from controls. When all subjects taken together were grouped according to triglyceride levels, it was found that small VLDL from hypertriglyceridaemic individuals suppressed the HMG-CoA reductase activity more than small VLDL from normotriglyceridaemic individuals. The opposite pattern was seen for LDL. The lipoprotein composition was related to the respective HMG-CoA reductase activity. In addition to a positive association between the cholesterol content of small VLDL and LDL, and the inhibition of HMG-CoA reductase activity, the apo C I and C II content of small VLDL and IDL was inversely related to the suppression of HMG-CoA reductase activity. This study shows that the cellular processing of apo B-containing lipoproteins in young post-infarction patients and healthy controls is heterogeneous and dependent on the composition of the lipoprotein.

The affinity of low-density lipoproteins and of very-low-density lipoprotein remnants for the low-density lipoprotein receptor in homozygous familial defective apolipoprotein B-100

We have identified two familial defective apo B-100 (FDB) homozygotes by DNA sequencing and have measured affinity of low-density lipoproteins (LDL) and very-low-density lipoprotein (VLDL) remnants for the LDL receptor in vitro. The patients were a 66-year-old man with coronary heart disease (plasma cholesterol level, 9.5 mmol/l before treatment) and his 69-year-old sister, without signs of cardiovascular disease (plasma cholesterol, 12.0 mmol/l before treatment). In both patients, treatment with statins caused a marked fall in plasma cholesterol level. Binding affinity of LDL from the two patients was 10%-20% of normal at 4 degrees C and 37 degrees C. Binding affinity of VLDL remnants was normal. We conclude that (1) residual affinity of LDL in homozygous FDB is high enough to permit significant catabolism via the LDL-receptor pathway, and (2) normal affinity of VLDL remnants permits normal hepatic clearance of precursors of LDL and increased clearance of LDL precursors when receptor activity is stimulated by statins. Residual affinity of LDL and normal affinity of remnants could explain why expression of the FDB mutation is generally milder than that of LDL receptor mutations causing familial hypercholesterolaemia.

Identification of the apo B-3500 mutation in the Norwegian population

Familial defective apolipoprotein B-100 (FDB) is caused by a mutation in codon 3500 of the apo B gene. It is inherited in a co-dominant fashion and is characterized by hypercholesterolaemia. Thus, FDB has similar features to familial hypercholesterolaemia (FH). In order to investigate whether some of the Norwegian subjects diagnosed as having FH actually have FDB, we have screened 208 Norwegian FH heterozygotes for the apo B-3500 mutation. One of the subjects possessed the mutation which was on a haplotype compatible with the mutation-bearing haplotype found in other populations. Although, hypercholesterolaemia segregated with haplotypes both at the apolipoprotein B and low density lipoprotein (LDL) receptor loci in the proband's family, LDL receptor analysis revealed that the proband was not doubly heterozygous for FDB and FH.

Familial Hypercholesterolaemia Regression Study: a randomised trial of low-density-lipoprotein apheresis

Low-density-lipoprotein (LDL) apheresis has the theoretical advantage over anion-exchange resins and hydroxymethylglutaryl coenzyme A inhibitors of decreasing lipoprotein(a) as well as LDL. To confirm this advantage, patients with heterozygous familial hypercholesterolaemia and coronary artery disease were randomised to receive LDL apheresis fortnightly (with disposable dextran sulphate/cellulose columns) plus simvastatin 40 mg daily, or colestipol 20 g plus simvastatin 40 mg daily. Quantitative coronary angiography was repeated after a mean of 2.1 years in 20 patients undergoing apheresis and in 19 on combination drug therapy. Changes in serum lipoproteins were similar in both groups apart from greater lowering by apheresis of LDL cholesterol (3.2 vs 3.4 mmol/L in drug group, p = 0.03) and lipoprotein(a) (geometric means 14 vs 21 mg/dL, p = 0.03). There were no significant differences in primary angiographic endpoints per patient but lesion-based and segment-based secondary endpoints were biased in favour of the drug group (change in minimum lumen diameter of lesions 0.07 vs -0.004 mm, p = 0.046; change in mean lumen diameter of segments 0.02 vs -0.06 mm, p = 0.01). None of the angiographic changes correlated with lipoprotein(a) concentrations. Per patient changes in % diameter stenosis and minimum lumen diameter in the two groups were as or more favourable than those observed in five published trials that assessed lipid-lowering drug therapy by quantitative coronary angiography. Although LDL apheresis combined with simvastatin was more effective than colestipol plus simvastatin in reducing LDL cholesterol and lipoprotein(a), it was less beneficial in influencing coronary atherosclerosis and should be reserved for patients unresponsive to drugs. Decreasing lipoprotein(a) seems to be unnecessary if LDL cholesterol is reduced to 3.4 mmol/L or less.

The A985G mutation in the medium-chain acyl-CoA dehydrogenase gene: high prevalence in the Swiss population resident in Geneva

We have determined the frequency of the A985G mutation in the medium-chain acyl-CoA dehydrogenase (MCAD) gene in a cohort of 1142 healthy babies born in two Geneva hospitals. Among babies with at least one Swiss parent, heterozygotes were detected at a frequency of 1/52, with a 95% confidence range from 1/82 to 1/38. The high frequency of the carrier state for this mutation suggests that MCAD-deficient babies are born with a frequency of 1/10,000 in the Swiss population. This number is in sharp contrast with the low number of symptomatic MCAD-deficient patients diagnosed in this country. Thus, the fraction of homozygotes who remain asymptomatic is likely to be very high in the Swiss population, and possibly higher than in other countries of northern Europe.

Phenotypic expression and frequency of familial defective apolipoprotein B-100 in Belgian hypercholesterolemics

DNA screening for apolipoprotein (apo) B mutations causing familial defective apolipoprotein B-100 (FDB) was performed in 87 hyperlipidemic Belgian individuals using heteroduplex analysis. Eighteen FDB heterozygotes from 5 unrelated families were identified. Three of the index cases reported an early family history of premature coronary heart disease (CHD). The frequency of the apo B3500 mutation was 8% in Belgians with type IIa hyperlipidemia, indicating that the prevalence of FDB may be as high as 1 in 250 in the general Belgian population. Plasma lipid levels of the patients identified in the present study are similar to those previously reported for FDB heterozygotes. We compared these data with results obtained in a genotype/phenotype correlation study of heterozygous familial hyper-cholesterolemia (FH) in the Afrikaner population of South Africa. Plasma cholesterol levels in FDB heterozygotes were similar to those reported for FH heterozygotes with defective receptors (Asp206-->Glu, approximately 20% normal receptor activity), but significantly lower than in FH heterozygotes with a mutant protein which virtually lacks receptor activity (Val408-->Met, < 2% normal receptor activity). FDB appears to be a significant genetic cause of hypercholesterolemia in Belgium.