Identification of a heterozygous compound individual with familial hypercholesterolemia and familial defective apolipoprotein B-100

Summary Familial defective apolipoprotein B-100 (FDB) is a recently identified dominantly inherited genetic disorder, which leads to increased serum levels of low density lipoprotein (LDL) cholesterol with reduced affinity for the LDL receptor. This genetic disorder is characterized by defective binding of the apolipoprotein B-100 (apo B-100), which is virtually the sole protein constituent of LDL, to the LDL receptor. The defective binding results from a G to A mutation at amino acid 10708 in exon 26 of the apolipoprotein B (apo B) gene creating a substitution of glutamine for arginine in the codon for amino acid 3500. It is postulated that FDB can exhibit the same clinical features as familial hypercholesterolemia (FH) caused by a defective LDL receptor. The purpose of this paper is to report on an individual with a defective LDL and a defective LDL receptor. The clinical features of this individual were the same as in the family members with either defective LDL or a defective LDL receptor: premature arcus lipoides, tendon xanthomata, and premature atherosclerosis. Although the clinical features were present to the same degree as in individuals with either defect the prognosis and treatment of such an individual could be different.Abbreviations FDB familial defective apolipoprotein B-100 - FH familial hypercholesterolemia - LDL low density lipoprotein - PCR polymerase chain reaction     

Italian familial defective apolipoprotein B patients share a unique haplotype with other Caucasian patients

Familial defective apolipoprotein (apo) B-100 together with familial hypercholesterolemia are the two common genetic conditions that cause hypercholesterolemia. familial defective apolipoprotein B-100 is due to mutations around codon 3500 of the apo B gene. The most-characterized mutation is a G>A transition at nucleotide 10,708 that results in the substitution of arginine by glutamine at codon 3500 (Apo B Arg3500Gln). Two other mutations are caused by a C>T transition, one at nucleotide 10,800 (Apo B Arg3531Cys) and the other at nucleotide 10,707 (apo B Arg3500Trp). In the present study we describe three new Italian cases of familial defective apolipoprotein B-100 (Apo B Arg3500Gln), one from the Liguria region and two from Sicily, and the haplotype of the apo B gene co-segregating with the mutation. By screening two groups of probands, clinically diagnosed as having Familial Hypercholesterolemia (700 from mainland Italy and 305 from Sicily), the prevalence of familial defective apolipoprotein B-100 due to Arg3500Gln was found to be very low (0.28% and 0.65%, respectively). The Arg3531Cys mutation was not detected in any proband. In the three new families with Arg3500Gln mutation in the present study and in one previously described in Italy, the mutation was associated with a unique apo B haplotype, which is consistent with data previously reported for Caucasian patients [XbaI-, MspI+, EcoRI-, presence of the 5' signal peptide insertion (Ins)allele, and the 49-repeat allele of the 3'-VNTR]. Received: 27 February 2001 / Accepted: 24 September 2001     

Phenotypic expression in double heterozygotes for familial hypercholesterolemia and familial defective apolipoprotein B-100

Variability in the expression of monogenic lipid disorders may be observed in patients carrying the same DNA mutation, suggesting possible genetic or environmental interactions. Our objective was to investigate the genotype-phenotype relationships in two unrelated French patients with an aggravated expression of a dominantly inherited hypercholesterolemia. In probands, segregation analysis complemented by DNA sequencing identified heterozygous defective alleles and mutations on two nonallelic loci for two monogenic lipid disorders: familial hypercholesterolemia at the low density lipoprotein (LDL) receptor locus and familial defective apolipoprotein B-100 at the locus encoding its ligand, apolipoprotein B-100. The LDL-receptor missense mutations had been reported in French Canadians. The apolipoprotein B mutation was the Arg3500Gln founder mutation in Northern Europe. Probands had an unusual phenotype of aggravated hypercholesterolemia that was complicated with premature coronary arterial disease, although remaining responsive to lipid-lowering drugs. This phenotype was distinct from that observed in their heterozygous relatives and distinct from those observed in FH or FDB homozygotes. These cases refer to a new class of patients with digenic lipid disorders, defined by specific clinical features that result from the combined effects of two independent loci. Moreover, the observed phenotype of aggravated hypercholesterolemia gives further evidence that receptor and ligand play distinct roles in regulating LDL metabolism. Although uncommon, these cases give insight into the molecular mechanisms that underly the clinical variability of inherited hypercholesterolemia. © 1996 Wiley-Liss, Inc.     

Familial defective apolipoprotein B-100: A review

Familial defective apolipoprotein B-100 (FDB) is an autosomal dominant genetic disorder of lipid metabolism associated with hyperlipidemia and elevated risk for atherosclerosis. FDB is caused by mutations in APOB reducing the binding affinity between apolipoprotein B-100 and the low-density lipoprotein receptor. Population studies suggest that approximately 0.1% of Northern Europeans and US Caucasians carries the R3500Q variant in APOB most commonly associated with FDB; in addition, the APOB R3500 W variant is known to make a significant contribution to familial hypercholesterolemia (FH) among East Asians. However, the elevation of plasma low-density lipoprotein cholesterol observed in FDB is frequently milder than that of FH due to mutations in LDLR, and FDB is subsequently underdiagnosed according to standard FH diagnostic criteria.     

Evaluation of a clinically applicable mutation screening technique for genetic diagnosis of familial hypercholesterolemia and familial defective apolipoprotein B

We have recently developed a simple mutation screening assay based on the denaturing gradient gel electrophoresis (DGGE) technique for detection of mutations in the coding and regulatory regions of the low density lipoprotein receptor (LDLR) gene and the codon 3500 region of the apolipoprotein (apo) B-100 gene leading to familial hypercholesterolemia (FH) and familial defective apo B-100 (FDB), respectively. To evaluate the assay, 14 Danish families suspected of FH were studied. In ten families, the DGGE assay detected seven different point mutations, including mutations undescribed prior to establishing the assay. In addition, in one of these ten families and in one of the remaining four families, Southern blotting detected the FH-DK3 exon 5 deletion. Based on segregation analysis and clinical data, the FH diagnosis was dubious in the remaining three families without DGGE or Southern blotting detectable mutations.
In conclusion, a simple DGGE based mutation screening assay may detect underlying mutations in most FH/FDB families, thus allowing its routine use in genetic counselling of FH-families.     

The effect of the apolipoprotein E polymorphism on lipid levels in patients with familial defective apolipoprotein B-100

Summary Serum lipid concentrations of patients with familial defective apolipoprotein B-100 (FDB) show a high interindividual variability although the underlying defect is caused by a single point mutation. On the other hand, several genetic factors modulating serum cholesterol levels are known, such as DNA polymorphisms of the apopolipoprotein B or the apolipoprotein E (apo E) gene. To assess the effect of the apo E polymorphism on serum cholesterol, lipid levels of FDB patients (n=36) were compared with those of a normolipidemic control group (n=272) according to their apo E genotype. For the FDB group mean values of low-density lipoprotein (LDL) cholesterol (mg/dl) were 225.7 ± 53.7 for E3/2 genotype (n = 3), 234.2±48.3 for E3/3 genotype (n=20), and 252.4±73.8 for E4/3 genotype (n=13). Means of triglycerides (mg/dl) were 121.0±21.2, 114.8± 60.7, and 110.0 ± 62.8 for the respective apo E genotypes. The calculated average effect of the apo E alleles on LDL cholesterol levels was –6.0% for allele e2 and +3.7% for e4 relative to the whole FDB group. The effect on triglyceride levels was +7.5% for e2 and –3.6% for e4. The control group showed a similar variation in LDL cholesterol depending on the different apo E genotypes. About 6% of the total variation in LDL cholesterol can be accounted for by the apo E locus in normolipidemic and hypercholesterolemic individuals alike.Abbreviations FDB familial defective apolipoprotein B-100 - apo apolipoprotein - LDL low-density lipoprotein - VLDL very low density lipoprotein - HDL high-density lipoprotein - PCR polymerase chain reaction Dedicated to Prof. Dr. N. Zöllner on the occasion of his 70th birthday     

Screening for the apolipoprotein B-100 arginine3500→ glutamine mutation in patients with type III hyperlipoproteinemia

Forty-three patients with clinically and biochemically unequivocally defined type III hyperlipoproteinemia (HLP) were screened for the presence of the apolipoprotein (apo) B-100 arginine3500-->glutamine mutation. This receptor-binding defective apolipoprotein B variant is the cause of familial defective apo B-100 (FDB), an autosomal dominantly inherited disease, which leads to increased plasma cholesterol levels and premature atherosclerosis. Neither patient expressed FDB. It is concluded that the gene defect responsible for FDB is not involved in the pathogenesis of type III HLP.     

Familial defective apolipoprotein B-100: a common cause of primary hypercholesterolemia

Summary Familial defective apolipoprotein B-100 (FDB) is a recently identified dominantly inherited genetic disorder characterized by a decreased binding of low density lipoprotein (LDL) to the LDL receptor due to defective apo B-100. FD B is caused by a G to A mutation at nucleotide 10 708 in exon 26 of the apo B gene creating a substitution of glutamine for arginine in the codon for amino acid 3500. The arginine₍₃₅₀₀₎ glutamine mutation has been observed in several populations in North America and Europe with a similar frequency of approximately 1/500 to 1/700. Haplotype analysis has demonstrated that the arginine₍₃₅₀₀₎ glutamine mutation occurs on the same chromosomal background. The fact that all individuals with FDB are of Caucasian extraction implies that the mutation has its origin in this population. The arginine₍₃₅₀₀₎ glutamine mutation has a profound impact of varying strength on the plasma LDL cholesterol level, leading to heterogeneous clinical expression comparable to classic familial hypercholesterolemia (FH) caused by a defective LDL receptor: tendon xanthoma, premature atherosclerosis and arcus lipoides. The present data suggest that the combination of these clinical features is no longer appropriate for the diagnosis of LDL-receptor-defective FH, but may be a common feature of a defective LDL receptor pathway originating either from defective LDL receptors or from malfunctioning ligand apo B-100.Abbreviations apo B-100 apolipoprotein B-100 - CAD coronary artery diseae - FDB familial defective apolipoprotein B100 - FH familial hypercholesterolemia - HDL high density lipoprotein - HL hyperlipidemia - LDL low density lipoprotein - PAD peripheral artery disease - PCR polymerase chain reaction - VLDL very low density lipoprotein     

Familial ligand-defective apolipoprotein B-100: Simultaneous detection of the ARG3500→GLN and ARG3531→CYS mutations in a French population

Familial ligand-defective apolipoprotein B-100 (FDB) is an autosomal dominant disorder leading to plasma LDL cholesterol elevation and coronary artery disease (CAD). Two specific mutations in the APOB gene—R3500Q and R3531C—induce FDB. We report an original method to detect both mutations simultaneously, based upon PCR-mediated, site-directed mutagenesis and double restriction of a unique PCR product. With this method we have investigated the prevalence of these mutations in 1,040 French patients. The R3500Q mutation was found in five probands. Genotypes were determined for 10 APOB polymorphic markers and were consistent with the common European ancestral haplotype previously reported. The only exception was one FDB proband who did not harbor the 48 repeat allele of the 3′HVR. Additionally, the first two R3531C mutations were identified in French probands. Genotypes were consistent with a previously reported haplotype, suggesting that this is another mutation of European ancestry. Hum Mutat 10:160–163, 1997. © 1997 Wiley-Liss, Inc.     

Effect of pravastatin on metabolic parameters of apolipoprotein B in patients with mixed hyperlipoproteinemia

Summary 3-Hydroxy-3-methylgluratyl coenzyme A reductase inhibitors reduce plasma cholesterol in different forms of hyperlipoproteinemia. Although an increase in low-density lipoprotein (LDL) receptor activity is the proven mechanism of this therapy in familial hypercholesterolemia, the mechanism remains controversial in mixed hyperlipoproteinemia. A decreased production of apolipoprotein B (apoB) and/or an increased removal of lipoproteins could mediate the hypocholesterolemic effect of these drugs. The effect of pravastatin on the metabolism of apoB was evaluated in a randomized, double blind, placebo controlled, cross-over study in five men with mixed hyperlipoproteinemia. Metabolic parameters for apoB were determined using endogenous labeling with [1^t3C]leucine and [¹⁵N]glycine and multicompartmental modeling. During pravastatin therapy cholesterol, LDL cholesterol, apoB, and LDL apoB levels were significantly reduced (P < 0.01) by 18%, 20%, 27%, and 29%, respectively, while triglyceride and high-density lipoprotein cholesterol levels remained unchanged. Pravastatin therapy increased the fractional catabolic rate of very low density lipoprotein apoB from 3.9±0.6 to 5.1±1.7 per day (P = 0.08) and that of LDL apoB from 0.37±0.09 to 0.46±0.10 per day (P<0.01). The apoB production (placebo 35.2±11.9 mg/kg per day; pravastatin 25.8±8.7 mg/kg per day) and conversion of very low density lipoprotein apoB to LDL apoB (placebo 65%, pravastatin 57%) remained stable. Thus, also in mixed hyperlipoproteinemia 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase the catabolism of apoB-containing lipoproteins without significantly affecting the production of apoB.Abbreviations apoB apolipoprotein B - FCR fractional catabolic rate - HMG hydroxy-methylglutaryl - CoA coenzyme A - FH familial hypercholesterolemia - HDL high-density lipoprotein - IDL intermediate-density lipoprotein - LDL low-density lipoprotein - VLDL very low density lipoprotein Dedicated to Prof. Dr. G. Paumgartner on the occasion of his 60th birthday     

The influence of simvastatin alone or in combination with gemfibrozil on plasma lipids and lipoproteins in patients with type III hyperlipoproteinemia

Summary Nineteen adult patients with type III hyperlipoproteinemia (HLP) and homozygosity for apolipoprotein (apo) E2 were treated with the 3-hydroxy-3-methyl glutaryl coenzyme A (HMG CoA) reductase inhibitor simvastatin (20 or 40 mg per day) alone or in combination with the fibrate derivative gemfibrozil (450 mg per day) during a 30-week outpatient study. With the 20-mg dose (n = 19) the mean plasma cholesterol level decreased from 13.24±8.04 8.04 at baseline to 8.04±4.19 mmol/l (mean reduction 39.3%; P<0.05), and the mean plasma triglyceride level decreased from 13.47±19.22 to 7.84±7.71 mmol/l (–41.8%; NS); this was due to a decrease in very low density lipoprotein (VLDL) cholesterol from 8.95±8.64 to 4.94±4.24mmo1/l (–44.8%; NS), a decrease in low density lipoprotein (LDL) cholesterol from 3.54±0.93to 2.25 ± 0.59 mmol/l (–36.5%; P<0.01), and an increase in high density lipoprotein (HDL) cholesterol from 0.72±0.28 to 0.85±0.34 (+18.1%; NS). Thirteen patients were treated with 40 mg simvastatin per day. Under this regimen there was a further significant decrease in LDL cholesterol from 2.33±0.62 to 1.81±0.49 mmol/l (–22.3%; P<0.01). In six patients who remained hyperlipidemic on monotherapy combination drug therapy with simvastatin (40 mg per day) and gemfibrozil (450 mg per day) was given. Compared to simvastatin alone the addition of gemfibrozil further lowered plasma concentrations of total cholesterol by 14.9%, VLDL cholesterol by 23.5%, and triglycerides by 17.1%, although this was not statistically significant. No patient was discontinued from single or combination drug therapy, and no severe clinical or biochemical side effects were observed. The results of this study demonstrate the usefulness of simvastatin in the therapy of type III HLP and indicate that in individual patients who remain hyperlipidemic on monotherapy combination drug therapy with both of these drugs is effective in further reducing plasma concentrations of total cholesterol, VLDL cholesterol, and triglycerides. Although no patient in this investigation developed myopathy or rhabdomyolysis, combined fibrate-HMG CoA reductase inhibitor treatment should be considered only for severe forms of hyperlipidemia and for patients who do not respond sufficiently to mon-therapy of any of these drugs.Abbreviations Apo Apolipoprotein - CPK creatine phosphokinase - GGT gamma-glutamyl transpeptidase - HDL high density lipoproteins - HLP hyperlipoproteinemia - HMG CoA 3-hydroxy-3-methyl glutaryl coenzyme A - IDL intermediate density lipoproteins - LDL low density lipoproteins - TG triglycerides - VLDL very low density lipoproteins     

Pharmacokinetic and pharmacodynamic assessment of alirocumab in patients with familial hypercholesterolemia associated with proprotein convertase subtilisin/kexin type 9 gain-of-function or apolipoprotein B loss-of-function mutations

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Allele-specific competitive blocker PCR: A one-step method with applicability to pool screening

We have developed a novel one-step pool screening PCR procedure which is based on the principles of amplification refractory mutation system (ARMS) and competitive oligonuleotide priming (COP) PCR. In addition to the usual primers, this approach uses two allele-specific competitive oligonucle-otides, one of which is 3′-end labeled with a dideoxynucleotide and blocks amplification of the wild-type allele. An allele-specific product is generated only in the presence of the mutation. The introduction of an allele-specific competitive blocker oligonucleotide improves the specificity and robustness of ARMS-PCR. Further its sensitivity is dramatically increased, which allows detection of one mutant allele in a large excess of wild-type-bearing genomic DNA by electrophoresis in an ethidium bromide- -stained agarose gel (up to 1 in 10⁴ alleles). This makes the method ideal for nonradioactive pool screening. The successful application of the method has been demonstrated for four different point mutations, two in the apolipoprotein B gene (R3500Q, R3531C) which result in familial defective apolipoprotein B-100, one in the CFTR gene (R1162X), and one in the gene for lipoprotein lipase (G188E). © 1995 Wiley-Liss, Inc.     

Long-term effect of lovastatin alone and in combination with cholestyramine on lipoprotein (a) level in familial hypercholesterolemic subjects

Summary We have determined the effect of lovastatin alone or in combination with cholestyramine on lipoprotein (a) [Lp(a)] levels in 59 heterozygotes for familial hypercholesterolemia (FH) treated for 33.8 (±6.1) months. The median pretrial Lp(a) value was 10.2 mg/100 ml, which is twice the median value in healthy people examined at the Institute of Medical Genetics, University of Oslo. The median Lp(a) level was insignificantly reduced by 10.3% during the first 20 weeks when the subjects were on a standardized medication of increasing doses of lovastatin and cholestyramine. The first 20 weeks were followed by usual care treatment period, and a further decrease in Lp(a) level to 16.2% (P=0.0012) was observed at the end of the study. Comparison between the 20 subjects on lovastatin monotherapy and the 31 subjects on the combined therapy of lovastatin and cholestyramine, revealed that the subjects on monotherapy had a median reduction of 20.1%, and the subjects on the combined therapy had a reduction of 15.4%. Thus, it appears that the reduction in Lp(a) level could be ascribed to lovastatin alone.Abbreviations ALAT alanine aminotransferase - ALP alkaline phosphatase - ASAT aspartate aminotransferase - CK creatine phosphokinase - FH familial hypercholesterolemia - GT glutamyl transpeptidase - HDL high density lipoprotein - HMG CoA 3-hydroxy-3-methylglutaryl coenzyme A - LDL low density lipoprotein - Lp(a) lipoprotein (a) - apo(a) apoprotein (a)     

Beneficial effects of pravastatin in peri- and postmenopausal hyperlipidemic women: a 5-year study on serum lipid and sex hormone levels

Objectives: The aims of the present study are to assess the 5 year effects of pravastatin on serum lipids and lipoproteins in women around the menopause and to assess the effects of pravastatin on serum gonadotropins and sex steroid levels over a long-term period. Methods: We evaluated the long-term efficacy of pravastatin on serum lipid levels (total cholesterol, LDL-cholesterol, HDL-cholesterol, triglyceride) in 121 patients (47 premenopausal and 74 postmenopausal women) suffering from primary hypercholesterolemia. The effects of this lipid-lowering drug on serum gonadotropins and sex steroids (estradiol, estrone, and testosterone) are also reported. Results: Pravastatin produced a remarkable reduction in the serum total cholesterol level of 19.2±9.3% (P<0.0001) and 18.9±11.8% (P<0.0001), and in LDLl-cholesterol of 25.1±18.7% (P<0.0001) and 24±18.0% (P<0.0001) after 24 and 60 months’ treatment, respectively. In hypertriglyceridemia, pravastatin also produced a remarkable reduction in triglyceride of 29.3±27.3% (P<0.0001) and 39.9±20.4% (P<0.0001) after 24 and 60 months of treatment, respectively. We found that serum gonadotropins and sex steroid levels changed naturally as a function of age from pre-therapy levels in the premenopausal patients after 60 months of treatment. Conclusions: Pravastatin was well tolerated over 5 years and was a very effective lipid-lowering agent for both hypercholesterolemia and hypertriglyceridemia with no effect on the biosynthesis of sex steroids. These findings suggest that pravastatin can be used in the treatment of hypercholesterolemia with/without high triglyceride levels in women around the menopause.