Familial Defective Apolipoprotein B-100 Research Articles

VII. Management of Specific Dyslipidemias

Randomized clinical trials generally have not focused on specific dyslipidemias. Yet these disorders are common enough to deserve specific attention in ATP III. In this section, the major dyslipidemias will be reviewed. Recommendations for their management are derived from the considered judgment of the ATP III panel. Recommendations are based in part on the sizable body of literature that describes changes in serum lipid and lipoprotein levels produced by dietary and drug therapies. In some dyslipidemias, combined drug therapy is required to obtain optimal lipoprotein profiles. In general, improvements in lipoprotein profiles rather than favorable clinical outcomes are the endpoints that serve as the basis for recommendations. These recommendations are made with the recognition that some induced changes in the lipoprotein profile have not been proven through clinical trial to reduce risk for CHD. Instead, they generally represent a synthesis of several lines of indirect evidence. Severe forms of elevated LDL cholesterol are defined as those in which LDL concentrations are persistently ≥190 mg/dL after TLC. Most elevations of this degree have a strong genetic component. Table VII.1-1 identifies three familial forms of elevated LDL cholesterol, i.e., familial hypercholesterolemia (heterozygous and homozygous forms), familial defective apolipoprotein B-100, and polygenic hypercholesterolemia. Clinical features, clinical outcomes, and therapeutic considerations are listed in the table and are discussed in more detail below. View this table: Table VII.1-1. Familial Disorders That Cause Very High LDL-Cholesterol Levels (≥190 mg/dL) ### a. Familial hypercholesterolemia (FH) Heterozygous familial hypercholesterolemia . This autosomal-dominant disorder occurs in 1 of every 500 people.917 The defect is a mutation in the gene for the LDL receptor;8 a large number of mutations affecting LDL receptor function has been reported.918,919 In all of these, half the normal number of receptors are expressed. Hypercholesterolemia often is detectable at birth or shortly thereafter, and total cholesterol levels eventually rise to 350-500 mg/dL …

Familial defective apolipoprotein B-100 versus familial hypercholesterolemia: An assessment of risk

Familial defective apolipoprotein B-100 versus familial hypercholesterolemia: An assessment of risk

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 2.8×10 −5 (95% CI, −3.1×10 −4 to 3.7×10 −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.

Intima-media thickness and atherosclerotic plaques in familial defective apolipoprotein B-100 and familial hypercholesterolemia.

Familial defective apolipoprotein B-100 (FDB) is a genetic disorder characterized by a decreased binding of low-density lipoprotein (LDL) particles to the LDL receptor due to defective apo B-100. Impaired LDL clearance could also be due to defects of the LDL receptor (familial hypercholesterolemia, FH). FDB was suggested to be clinically indistinguishable from classical FH. The measurement of the intima-media thickness (IMT) is an accepted method for the direct evaluation of early atherosclerosis. Thus, the aim of this study was to examine the IMT in patients with FDB in comparison to FH. Our data indicate that IMT in FDB does not differ from IMT in FH.

Comparison of apolipoprotein B metabolism in familial defective apolipoprotein B and heterogeneous familial hypercholesterolemia

Both defective LDL receptors (familial hypercholesterolaemia, FH) and mutations in apolipoprotein B (apoB) on LDL (familial defective apoB, FDB) give rise to a phenotype of elevated LDL cholesterol. We sought to compare the metabolic basis of the two conditions by examining apoB turnover in FDB and FH subjects. A group comprising three heterozygous and one homozygous FDB subjects were compared with five FH heterozygotes and 17 control subjects using a deuterated leucine tracer. Kinetic parameters were derived by multicompartmental modelling. FH heterozygotes had a reduced delipidation rate for VLDL, which led to a moderate increase in plasma triglyceride. Compared with controls and FH, the FDB subjects converted 44% less IDL to LDL. The LDL FCR was reduced to a similar extent in FDB and FH. In all subjects LDL plasma levels appeared to be regulated by the LDL FCR and the rate of production of small VLDL. We conclude that disturbances in IDL metabolism provide the basis for understanding why FDB is less severe than FH. Our findings suggest that an apoB-LDL receptor interaction is important in the IDL to LDL conversion.

Genotyping of the Apolipoprotein B R3500Q Mutation Using Immobilized Locked Nucleic Acid Capture Probes

Hyperlipidemia and coronary heart disease (CHD) are associated with genetic variation in the apolipoprotein B (apoB) gene (1). Nonexchangeable apolipoprotein B-100 (ApoB-100) is an important determinant of LDL-cholesterol in plasma; it plays a central role in cholesterol transport by its association to LDL particles as a ligand for the LDL receptor (2). One of the first mutations in the apoB gene to be discovered was the ApoB-100 R3500Q (apoBR3500Q) mutation (3), a single nucleotide transition, CGG to CAG, in exon 26. This mutation reduces the affinity to the LDL receptor by at least 95% (4) and is the major cause of familial defective ApoB-100 (FDB). The frequency of the mutation is 1:500 to 1:700 in Caucasians (5)(6). Because the cholesterol concentration is often within the reference interval in FDB patients, the only reliable way of detecting FDB is by genotyping. At present, genotyping of the apoBR3500Q mutation is based on PCR (7)(8)(9), but other methods, such as heteroduplex analysis and real-time PCR, have also been applied (10)(11)(12). In general, these methods are time-consuming and need to be optimized. Here we describe a simple, rapid, and sensitive assay for genotyping the apoBR3500Q mutation that is suitable for the 96-well microtiter plate format and relies on hybridization of PCR amplicons to allele-specific locked nucleic acid (LNA) capture probes (13)(14). The microtiter plates were prepared by covalent photoimmobilization of 10 pmol/well of either wild-type (wt)-LNA8 [AQ-CONH-(CH2)3-TACATGTTATGCTGA-GLALMeCLMeCLGLTLGLTLG] or mutant (m)-LNA8 [AQ-CONH-(CH2)3-TACATGTTATGCTGA-GLALMeCLTLGLTLGLTLG] capture probes using an …

Molecular basis of familial hypercholesterolemia in Brazil: Identification of seven novel LDLR gene mutations.

Low-density lipoprotein receptor (LDLR) gene mutations cause familial hypercholesterol-emia (FH), one of the most common single gene disorders. The spectrum of LDLR mutations in Brazil is not known. The aim of this study was the characterization of LDLR mutations in 35 unrelated Brazilian patients with heterozygous FH. The promoter region, the 18 exons and the flanking intron sequences of the LDLR gene were screened by PCR-SSCP analysis and by DNA sequencing. In addition, we have screened the apolipoprotein B gene (APOB) for known mutations (R3500Q and R3531C) that cause Familial defective apo B-100 (FDB) by PCR-RFLP procedure. We found two nonsense (E92X and C371X) and six missense LDLR mutations (R236W, G322S, G352D, A370T, C675W and C677Y), that were previously described in FH patients from other populations. We also found five novel missense [G(-20)R, T476P, V503G, D580H and S652R] and two novel frame shift LDLR mutations (FsR757 and FsS828). Four patients were found to carry two different mutations in the LDLR gene: G352D and A370T (one patient), S652R and C675W (one patient) and T476P and V503G (two patients). APOB mutations were not found. These findings demonstrate that there is a broad spectrum of mutations in the LDLR gene in FH individuals from Brazil.

Low-density lipoprotein receptor gene mutation analysis and clinical correlation in Belgian hypercholesterolaemics

It is generally believed that patients with familial hypercholesterolaemia (FH) have a higher cardiovascular risk than hypercholesterolaemics without a defect in the low-density lipoprotein receptor (LDLR) gene. However, no conclusive evidence to support this view has yet been presented. We investigated this aspect in Belgian hyperlipidaemics as part of a comprehensive effort to determine the impact of FH in this population. DNA samples of 98 unrelated Belgian patients with a family history of autosomal dominant hypercholesterolaemia were screened for mutations in the LDLR gene, after exclusion of known mutations causing familial defective apolipoprotein B-100 (FDB). Eight of the 22 distinct LDLR gene mutations identified in 27 subjects have not previously been described in other populations. As expected, the mutation-positive patients had a significantly worse lipid profile than the mutation-negative subjects (p<0·05), but this did not correlate with clinical cardiovascular status. In conclusion, the presence of a mutation in the LDLR gene was not a reliable predictor of cardiovascular risk in the hyperlipidaemic subjects included in this study. However, it is possible that prolonged exposure to the high levels of LDL cholesterol in genetically proven FH patients will in future cause a higher incidence of coronary heart disease. Our data may reflect the genetic heterogeneity of inherited hypercholesterolaemia, recently shown to be caused by several major genes.

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).

Apolipoprotein B Arg3500Gln mutation prevalence in children with hypercholesterolemia: a French multicenter study.

Familial defective apolipoprotein B-100, a dominantly inherited form of hypercholesterolemia caused by a single Arg3500Gln mutation, is silent in childhood but may confer a high risk of cardiovascular disease in adulthood. The objective was to determine the prevalence of familial defective apolipoprotein B-100 in hypercholesterolemic French children and to provide a basis for targeting screening efforts in this population. One hundred ninety children attending 13 pediatric clinics distributed throughout France were included based on the presence of type IIa hypercholesterolemia with a plasma low-density lipoprotein-cholesterol level of more than 130 mg/dL. The Arg3500Gln mutation was detected in dried blood spots using a polymerase chain reaction assay combined with enzymatic restriction. Three hyperlipidemia phenotypes were found: monogenic dominant pure hypercholesterolemia (n = 117), polygenic hypercholesterolemia (n = 43), and combined hyperlipidemia (n = 11). Three unrelated children were heterozygous for the Arg3500Gln mutation; all three had monogenic dominant pure hypercholesterolemia (3/94 families; 3.2%), yielding a prevalence of 1.83% (3/164) in hypercholesterolemic children, which is similar to prevalences reported in European adults. The familial defective apolipoprotein B-100 mutation was common (1/31) in children with a phenotype of familial hypercholesterolemia, supporting screening in this population with the goal of preventing premature cardiovascular events.

A molecular genetic service for diagnosing individuals with familial hypercholesterolaemia (FH) in the United Kingdom.

A genetic diagnostic service for familial hypercholesterolaemia (FH) has been established over the last 4 years in the Clinical Molecular Genetics Laboratory at Great Ormond Street Hospital for Children NHS Trust (GOSH), London. In total there have been 368 referrals; 227 probands and 141 family members, which have come from a number of lipid clinics and from general practitioners. FH is caused by mutations in the low-density lipoprotein receptor gene (LDLR) and these are analysed by SSCP, DNA sequencing and direct assays. The clinically indistinguishable disorder, familial defective apolipoprotein B100 (FDB) is caused by one of three mutations in the apolipoprotein B100 gene (APOB) which are analysed by direct assays. Mutations predicted to be pathogenic were found in 76 probands, 67 in LDLR (23 previously undescribed) and nine in APOB. The mutation detection rate was 53% in paediatric probands, 32% in adults with a 'definite' FH diagnosis (tendon xanthoma positive) and 14% in adults with a 'possible' FH diagnosis (tendon xanthoma negative). The predicted loss of sensitivity that would result from reducing the number of exons tested has been assessed, and a molecular screening strategy suitable for UK patients is proposed. A similar strategy may be useful for other countries where genetic heterogeneity results in a wide mutation spectrum for FH.

Compound Heterozygous Familial Hypercholesterolemia and Familial Defective Apolipoprotein B-100 Produce Exaggerated Hypercholesterolemia

Familial hypercholesterolemia (FH) and familial defective apolipoprotein B-100 (FDB) represent ligand-receptor disorders that are complementary. Individuals with both FH and FDB are unusual. We report a family with both disorders and the impact of the mutations on the phenotypes of the family members. We used single strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) for genetic analysis of all 18 exons and the promoter region of the LDL receptor and DGGE for genetic analysis of the apolipoprotein B-100 (apo B-100) gene. The functional significance of the apo B-100 mutation was studied using a U937 cell proliferation assay. Fasting serum lipid profiles were determined for the index case and seven first-degree relatives. One of the patient's sisters had a missense mutation (Asp(407)-->Lys) in exon 9 of the LDL receptor and a serum LDL-cholesterol concentration of 4.07 mmol/L. Four other first-degree relatives had hyperlipidemia but no LDL-receptor mutation. However, these subjects had a mutation of the apo B-100 gene (Arg(3500)-->Trp). The cell proliferation rate of U937 cells fed with LDL from other subjects with the same mutation was fourfold less than that of controls. The index case had both FH- and FDB-related mutations. Her serum LDL-cholesterol (9.47 mmol/L) was higher than all other relatives tested. Existence of both FH and FDB should be considered in families with LDL-receptor mutations in some but not all individuals with hypercholesterolemia or when some individuals in families with FH exhibit exaggerated hypercholesterolemia.

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.

Frequency of the R3500Q mutation of the apolipoprotein B-100 gene in a sample screened clinically for familial hypercholesterolemia in Hungary

Familial hypercholesterolemia (FH) and familial defective apolipoprotein B-100 (FDB) cause early onset of coronary heart diseases (CHD). According to the recommendations of the international MEDPED program, we tried to find FH cases. We analyzed 73 FH probands and their 304 first-degree relatives. A total of 39 probands were found from the 21 000 subjects screened (1:538) from family doctors’ registers recording all citizens, while the remaining 34 were derived from screened patients from lipid clinics. In our FH probands, four cases of FDB (R3500Q mutation) were diagnosed with allele-specific PCR, and the mutation was also detectable in five cases out of seven living family members. In the remaining 69 FH families, 156 people were diagnosed clinically with FH, and 31.8% of the males (against 13% of the not clinically diagnosed FH males, P<0.01), and 32.4% of the females (against 13.5% of the not clinically diagnosed FH females, P<0.01) suffered from early onset CHD. The plasma total cholesterol level of the FDB patients, especially in the younger patients, was very close to normal values. Therefore, the FDB patients seem to be under-represented in this type of survey. Because FDB is one of the independent causes of early onset CHD, the R3500Q mutation should be considered in families with a high frequency of cardiovascular diseases.

Mutation analysis in a small cohort of New Zealand patients originating from the United Kingdom demonstrates genetic heterogeneity in familial hypercholesterolemia

Familial hypercholesterolemia (FH) and familial defective apolipoprotein B-100 (FDB) are relatively common lipid disorders caused by mutations in the low-density lipoprotein receptor (LDLR) and apolipoprotein B (apo B) genes, respectively. Molecular analysis at these loci was performed in eight New Zealand subjects with clinical features of heterozygous FH. Utilization of an in vitro lymphocyte receptor assay demonstrated normal receptor function in four patients, three of whom screened positive for the founder-type apo B mutation, R3500Q, causing FDB. Four patients with reduced LDLR function, consistent with heterozygous FH, revealed three previously documented mutations in exons 3 (W66X), 6 (C292Y) and 7 (G322S) of the LDLR gene and, a novel 2-bp deletion (TC or CT) after nucleotide 1204 (or 1205) in exon 9. The remaining patient was found to be FH/FDB negative after extensive mutation screening using both denaturing gradient gel electrophoresis and heteroduplex-single strand conformation polymorphism analysis. Haplotype analysis at the LDLR and apo B loci finally excluded the likelihood that mutations in these two genes underlie the FH phenotype in the molecularly uncharacterized New Zealand family originating from the United Kingdom. This family represents a valuable source of material for future genetic dissection of autosomal dominant hypercholesterolemia (ADH), shown to be a heterogeneous disease through molecular analysis.

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.

Familial defective apolipoprotein B-100 in hypercholesterolemic patients in Poland

Familial defective apolipoprotein B-100 in hypercholesterolemic patients in Poland

Increased Production of HDL ApoA-I in Homozygous Familial Defective ApoB-100

Familial defective apolipoprotein (apo) B-100 (FDB) is a frequent cause of hypercholesterolemia. Hypercholesterolemia in homozygous FDB is less severe than in homozygotes for familial hypercholesterolemia. Recently, we showed decreased low density lipoprotein (LDL) apoB-100 fractional catabolism and decreased production of LDL due to an enhanced removal of apoE-containing precursors in a patient with homozygous FDB. The effects of defective apoB-100 on high density lipoprotein (HDL) metabolism are unknown. We studied HDL apoA-I metabolism in this FDB patient and in 6 control subjects by using (2)H(3)-L-leucine as a tracer. ApoA-I levels were normal in all study subjects. However, the fractional catabolic rate and the production rate of apoA-I were increased, by 79% and 70%, respectively, in FDB; the fractional catabolic rate of apoA-I in FDB was 0.34 day(-1) compared with 0.19+/-0.03 day(-1) in normal controls. The production rate of apoA-I in FDB was 18.4 mg. kg(-1). d(-1) compared with 10.8+/-2.3 mg. kg(-1). d(-1) in controls. Thus, we have shown for the first time that defective apoB-100 may influence HDL kinetics. The increase in total HDL turnover might enhance reverse cholesterol transport and could contribute to the seemingly benign clinical course of FDB compared with that of familial hypercholesterolemia.

Familial defective apolipoprotein B-100: a mutation emerged in the Mesolithic ancestors of Celtic peoples?

As part of the WHO MONICA project, plasma low density lipoprotein cholesterol (LDL-C) concentrations were determined in 3341 randomly selected individuals from Switzerland [ [1] Burnand B. Wietlisbach V. Riesen W. et al. Lipides sanguins dans la population suisse: enquête MONICA 1988–89. Schweiz. Med. Wschr. 1993; 123: 29-37 PubMed Google Scholar ]. Mean LDL-C was 16% higher than in US Caucasians, and 4–60% higher than in other European populations [ 1 Burnand B. Wietlisbach V. Riesen W. et al. Lipides sanguins dans la population suisse: enquête MONICA 1988–89. Schweiz. Med. Wschr. 1993; 123: 29-37 PubMed Google Scholar , 2 US Department of Health and Human Services, Lipid Research Clinics Program. Population Studies Data Book. Vol. I, The Prevalence Study. Washington DC: Public Health Service, National Institutes of Health (NIH 80-1527) 1980. p. 27-81. Google Scholar , 3 Verschuren W.M.M. Jacobs D.R. Bloemberg B.P.M. et al. Serum total cholesterol and long-term coronary heart disease mortality in different cultures. Twenty-five-year follow-up of the Seven Countries Study. J. Am. Med. Assoc. 1995; 274: 131-136 Crossref PubMed Google Scholar ]. If the cut-off of the National Cholesterol Education Program (LDL-C >4.14 mmol/l [ [4] Expert Panel on Detection Evaluation, and Treatment of High Blood Cholesterol in Adults. Summary of the second report of the National Cholesterol Education Program (NCEP) Expert Panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel II), J Am Med Assoc 1993;269(23):3015–3023. Google Scholar ]) is applied to US Caucasians, then 12–32% of males and 5–40% of females have elevated LDL-C [ [2] US Department of Health and Human Services, Lipid Research Clinics Program. Population Studies Data Book. Vol. I, The Prevalence Study. Washington DC: Public Health Service, National Institutes of Health (NIH 80-1527) 1980. p. 27-81. Google Scholar ], whereas in the Swiss, 31–56% of males and 14–66% of females have LDL-C above this cut-off [ [1] Burnand B. Wietlisbach V. Riesen W. et al. Lipides sanguins dans la population suisse: enquête MONICA 1988–89. Schweiz. Med. Wschr. 1993; 123: 29-37 PubMed Google Scholar ]. Although this data is based on a relatively small sample, it raises the question as to whether the higher prevalence of hypercholesterolemia in Switzerland compared to other populations is due to genetic differences.

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

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. 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 Arg(3500)-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 Arg(3500)-Gln mutation. Fluorescence was significantly increased in cells incubated with DiI-LDL in competition with unlabeled LDL from FDB(R3500Q) 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 Arg(3500)-Gln mutation had significantly reduced LDL ligand function. The binding affinity of LDL from FDB(R3500Q) 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. The diagnostic accuracy of the assay was too low to allow reliable diagnosis of individual cases of heterozygous FDB(R3500Q). However, fluorescence flow cytometry may supplement genetic identification of FDB and functionally characterize gene mutations associated with major reductions in LDL ligand function.