Co-segregation of elevated LDL with a novel mutation (D92K) of the LDL receptor in a kindred with multiple lipoprotein abnormalities

Factors predisposing to the phenotypic features of familial combined hyperlipidemia have not been clearly defined. In the course of investigating familial coronary artery disease in Utah, we identified a three-generation family in which multiple members were affected with type IIa hyperlipoproteinemia (HLP IIa), type IIb hyperlipoproteinemia (HLP IIb), or type IV hyperlipoproteinemia (HLP IV). Because several family members had relatively severe low-density lipoprotein (LDL) cholesterol elevation, in order to dissect the possible contribution to the plasma lipoprotein abnormalities in this pedigree, we identified a novel point mutation in the low-density lipoprotein receptor (LDLR) gene, a G-to-A transition at nucleotide position 337 in exon 4. This change substituted lysine for glutamic acid at codon 92 (D92K) of the LDL receptor. By means of mutant allele-specific amplification we determined that the mutation co-segregated with elevated cholesterol and LDL cholesterol in the plasma of family members with HLP IIa and HLP IIb, but not with the elevated plasma triglycerides seen in HLP IIb and HLP IV patients. Thus, in families with apparent familial combined hyperlipidemia, a defective LDLR allele and other genetic or environmental factors that elevate plasma triglycerides may account for the multiple lipid phenotypes observed in this kindred. Received: November 5, 1999 / Accepted: January 8, 2000     

Characterization of a disease-causing Glu119-Lys mutation in the low-density lipoprotein receptor gene in two Danish families with heterozygous familial hypercholesterolemia

Mutations in the gene for the low-density lipoprotein receptor (LDL receptor) cause the autosomal dominant inherited disease familial hypercholesterolemia (FH). In 15 Danish patients with heterozygous FH we have screened exon 4 of the LDL receptor gene for point mutations and small rearrangements employing genomic DNA amplification and bidirectional solid-phase sequencing. Two subjects were found to be heterozygous for a guanine to adenine base substitution at nucleotide position 418 of the LDL receptor cDNA. This point mutation results in an amino acid change from glutamic acid to lysine at amino acid residue 119 in the third repeat of the cysteine-rich ligand binding domain of the mature LDL receptor. Disruption of LDL receptor function by the Glu¹¹⁹-Lys mutation was confirmed by site-directed rnutagenesis and expression in COS-7 cells. By Western blotting the mutation was found to affect the processing of the LDL receptor protein. Using flow cytometric analysis of the transfected cells a decreased binding and internalization of LDL by the mutant receptor was documented. By means of a mutation-specific PCR-based assay the Glu¹¹⁹-Lys mutation was not detected in another 85 apparently unrelated Danish heterozygous FH patients. We identified six persons in the index families with the Glu¹¹⁹-Lys mutation cosegregating with the clinical syndrome of FH in these families. Furthermore, haplotype analysis revealed that the haplotype [SfaNI+, StuI+, AvaII–, (dTA)₇] of the mutation carrying allele was the same in the two apparently unrelated patients. This indicates that the mutation has been inherited from a common ancestor. © 1994 Wiley-Liss, Inc.     

Identification of the valine 408 to methionine mutation in the LDL receptor in a Greek patient with homozygous familial hypercholesterolemia

We have identified the cytosine to thymine change in the codon for amino acid 408 which causes valine to be replaced by methionine in exon 9 of the LDL receptor gene in a 12-year-old Greek boy living in Germany, with homozygous familial hypercholesterolemia, by using polymerase chain reaction-amplified genomic DNA and subsequent restriction digestion. Homozygosity was confirmed by direct DNA sequencing. The mutation was present in both his parents, and his brother, grandmother, uncle and cousin. Six restriction fragment length polymorphisms of the LDL receptor gene were used to determine the haplotype of the defective allele. The haplotype was different from the one reported earlier in African Afrikaners and from Holland. We conclude that the mutation in the Greek boy probably occurred as an independent mutation. Because the parents are from different areas in Greece, this mutation may be common in Greeks.     

Common founder mutation in the LDL receptor gene causing familial hypercholesterolaemia in the Icelandic population

Haplotype analysis in 18 apparently unrelated families with familial hypercholesterolaemia (FH) in Iceland has identified at least five different chromosomes cosegregating with hypercholesterolaemia. The most common haplotype was identified in 11 of the 18 families, indicating a founder mutation responsible for FH in the Icelandic population. By using single-strand conformation polymorphism (SSCP) and direct sequencing of amplified DNA, we identified a novel mutation (a T to a C) in the second nucleotide in the 5′ part of intron 4 in the LDL receptor gene. This mutation was present in ˜60% of the FH families (10/18), supporting the prediction of a common founder. These families could be traced to a common ancestor in half of the cases by going back no further than the eighteenth century. The mutation was predicted to affect correct splicing of exon 4, and analysis at the cellular level demonstrated an abnormal mRNA containing intron 4 sequence in lymphoblastoid cells from a patient carrying this mutation. Translation of the mRNA would lead to a premature stop codon and a truncated nonfunctional protein of 285 amino acids. The novel sequence change created a new restriction site for the restriction endonuclease NlaIII, and using this assay, 29 unrelated individuals with possible FH attending a lipid clinic for treatment were examined for this mutation. Two individuals in this group of patients were found to be carriers of this mutation, supporting the suggestion of a founder mutation. Using this assay for the detection of FH in the Icelandic population should identify > 60% of these individuals. Hum Mutat 10:36–44, 1997. © 1997 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)     

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     

丝瓜络对高脂血症小鼠LDL-R基因表达的影响

目的： 观察中药丝瓜络（RLF）对高脂血症小鼠低密度脂蛋白受体（LDL-R）基因表达的影响。方法：用高脂饲料喂养雄性昆明小鼠建立高脂血症模型,以血脂康作为阳性对照观察饲料中补充丝瓜络粉剂喂养对小鼠血清总胆固醇（TC）、低密度脂蛋白（LDL-C）的影响。按Trizol法提取小鼠肝脏总RNA,利用逆转录-聚合酶链反应(RT-PCR)测定LDL-R mRNA的表达,观察其在正常、高脂和给药3种条件下的差异。结果：（1）高脂组小鼠的血清TC和LDL-C分别为（5.71±0.82）和（3.99±1.12）mmol/L,显著高于正常对照组的TC（2.31±0.21）mmol/L和LDL-C（1.72±0.28）mmol/L（P＜0.01）,而高脂+丝瓜络组、高脂+血脂康组的TC分别为（3.65±0.28）mmol/L、（3.94±0.65）mmol/L和LDL-C分别为（2.74±0.54）mmol/L、（3.00±0.23）mmol/L,显著低于高脂组（P＜0.01）;（2）与正常对照组比较,高脂组小鼠肝脏LDL-R mRNA的表达减弱（P＜0.01）;与高脂组比较,高脂+丝瓜络组、高脂+血脂康组小鼠肝脏LDL-R mRNA的表达增强（P＜0.01）。结论： 丝瓜络对实验性高脂血症小鼠有明显的降血脂效应,且能使实验性高脂血症小鼠肝组织的LDL-R mRNA表达增强。     

Silent exonic mutations in the low-density lipoprotein receptor gene that cause familial hypercholesterolemia by affecting mRNA splicing

In a large group of patients with the clinical phenotype of familial hypercholesterolemia, such as elevated low-density lipoprotein (LDL) cholesterol and premature atherosclerosis, but without functional mutations in the genes coding for the LDL receptor and apolipoprotein B, we examined the effect of 128 seemingly neutral exonic and intronic DNA variants, discovered by routine sequencing of these genes. Two variants, G186G and R385R, were found to be associated with altered splicing. The nucleotide change leading to G186G resulted in the generation of new 3'-splice donor site in exon 4 and R385R was associated with a new 5'-splice acceptor site in exon 9 of the LDL receptor gene. Splicing of these alternate splice sites leads to an in-frame 75-base pair deletion in a stable mRNA of exon 4 in case of G186G and R385R resulted in a 31-base pair frame-shift deletion in exon 9 and non-sense-mediated mRNA decay.     

Identification of the serine-156 to leucine mutation in the low-density lipoprotein receptor in a German family with familial hypercholesterolemia

Summary Familial hypercholesterolemia is caused by various mutations in the gene encoding the low-density lipoprotein receptor. To date more than 100 mutations have been identified, including insertions and deletions as well as single base changes. In the German population haplotype analysis using four restriction fragment length polymorphisms has recently suggested that there exist at least six different genetic defects. Screening 100 FH patients of German origin for the serine 156 to leucine mutation, originally described in a Puerto Rican family living in the United States, resulted in the identification of the mutation in one family. However, by haplotype analysis the mutation was found on a different haplotype from that reported originally. Based on comparison of the haplotypes and their frequencies we suggest that this mutation has occurred independently at least twice.Abbreviations FH familial hypercholesterolemia - LDLR low-density lipoprotein receptor - PCR polymerase chain reaction - RFLP restriction fragment length polymorphism Dedicated to Prof. Dr. N. Zöllner on the occasion of his 70th birthday     

Screening for point mutations in the LDL receptor gene in Bulgarian patients with severe hypercholesterolemia

Familial hypercholesterolemia (FH) is a common, autosomal dominant disorder of lipid metabolism, caused by defects in the receptor-mediated uptake of LDL (low-density lipoproteins) due to mutations in the LDL receptor gene (LDLR). Mutations underlying FH in Bulgaria are largely unknown. The aim of the present study was to provide information about the spectrum of point mutations in LDLR in a sample of 45 Bulgarian patients with severe hypercholesterolemia. Exons 3, 4, 6, 8, 9, and 14, previously shown to be mutational hot spots in LDLR, were screened using PCR-single-strand conformation polymorphism (SSCP). Samples with abnormal SSCP patterns were sequenced. Three different, hitherto undescribed point mutations (367T>A, 377T>A, 917C>A) and two previously described mutations (858C>A and 1301C>T) in eight unrelated patients were identified; four of the detected point mutations being missense mutations and one, a nonsense mutation. One of the newly described point mutations (917C>A) is a base substitution at a nucleotide position, at which two other different base substitutions have already been reported. Thus, all three possible base substitutions at this nucleotide position have been detected, making it a hot spot for point mutations causing FH. This is the first such mutational hot spot described in exon 6 of LDLR.     

Polymorphisms at the SRBI locus are associated with lipoprotein levels in subjects with heterozygous familial hypercholesterolemia

Scavenger receptor, class B, type 1 (SRBI) is a promising candidate gene involved in the pathophysiology of atherosclerosis. We have examined the association of three common polymorphisms at the SRBI locus in 77 subjects who were heterozygous for familial hypercholesterolemia (FH). The alleles represented by polymorphisms in exon 1 and exon 8 were associated with variation in plasma concentrations of fasting triglyceride (TG). Mean plasma TG concentrations for homozygotes for the most common allele, and for heterozygotes and homozygotes for the less common allele were 85 +/- 6, 111 +/- 9 and 135 +/- 22 mg/dl (p = 0.011) for exon 1, and 96 +/- 11, 86 +/- 6 and 134 +/- 13 mg/dl (p = 0.007) for exon 8, after adjustment for age, sex and body mass index. In addition, the exon 8 polymorphism was associated with increased total cholesterol (320 +/- 15, 340 +/- 8 and 388 +/- 18 mg/dl, p = 0.015), very low density lipoprotein (VLDL) cholesterol (18 +/- 2.9, 15.7 +/- 1.6 and 33.4 +/- 3.9 mg/dl, p < 0.001) and low density lipoprotein (LDL) cholesterol (251 +/- 15, 270 +/- 8 and 312 +/- 10 mg/dl, p = 0.041) concentrations. In agreement with animal studies, our data also suggest a role for the SRBI in the metabolism of apolipoprotein B (apoB)-containing lipoproteins in humans. This pathway may constitute a backup mechanism to LDL receptor-mediated pathways for the catabolism of these lipoproteins, which could be particularly relevant in subjects with high levels of apoB-containing lipoproteins, such as those occurring in patients with FH.     

A novel deletion in the low-density lipoprotein receptor gene in a patient with familial hypercholesterolemia from Petersburg

Fifty St. Petersburg patients with type IIa hyperlipoproteinemia were screened for the presence of structural rearrangements in the low-density lipoprotein receptor (LDLR) gene. One novel deletion of the length about 5 kilobases (kb) was found. This deletion seems to remove completely exons 4, 5, and 6 from the LDLR gene, coding for the largest part of the receptor ligand-binding domain. © 1993 Wiley-Liss, Inc.     

JCL Roundtable: Diagnosis of severe familial hypercholesterolemia

The diagnosis of familial hypercholesterolemia is usually straightforward. The severely elevated low-density lipoprotein cholesterol and the occurrence of high concentrations of low-density lipoprotein cholesterol in the parents provide the diagnosis. The presence of tendon xanthomata is confirmation but not necessary. However, this relatively simple picture becomes much more complicated when one attempts to define the genetic variants that actually produced this clinical syndrome. In this Roundtable discussion, I am joined by two experts in the identification of genetic abnormalities discovered in those with phenotypic familial hypercholesterolemia. Dr. John Kane from the University of California, San Francisco, and Dr. Daniel Rader from the University of Pennsylvania share their knowledge in and experience with this topic.     

Long-term experience with extracorporeal low-density lipoprotein cholesterol removal by dextran sulfate cellulose adsorption

Summary Patients with familial hypercholesterolemia have a high incidence of coronary heart disease due to diet- and drug-resistant, elevated low-density lipoprotein cholesterol (LDL-C). Five patients with familial hypercholesterolemia and diet- and drug-resistant LDL-C > 230 mg/dl were treated by LDL apheresis using dextran sulfate cellulose adsorption (Liposorber System LA-15, Kaneka). Plasma separation was by 0.5-m² polysulfone hollow fiber filter. Two columns containing 150 ml of dextran sulfate cellulose alternately adsorbed LDL and were regenerated by 4.1% saline. The five patients received a total of 360 treatments at 7-day intervals. The treated plasma volume per session was 4.1 ± 0.41. Postapheresis values compared with preapheresis were: total cholesterol, 40%; LDL-C, 28%; VLDL-C, 65%; HDL-C, 95%; triglycerides, 70%; white blood cells, 116%; platelets, 87%; C3 complement, 79%; fibrinogen, 64%; albumin, 94%. The decrease in HDL-C per treatment was not significant. The safety parameters showed only slight changes. The initial LDL of 436 ± 172 mg/dl decreased to mean pre-apheresis levels of between 150 and 100 mg/dl. The anti-atherogenic HDL increased in three and remained unchanged in two patients. Adverse events like hypotension, angina pectoris, and technical problems occurred in 11 of the 360 treatments. Long-term treatment of patients with diet- and drug-resistant familial hypercholesterolemia by extracorporeal dextran sulfate cellulose adsorption is effective and safe.Abbreviations LDL low-density lipoprotein - LDL-C lowdensity lipoprotein cholesterol - VLDL very low-density lipoprotein - HDL high-density lipoprotein - HDL-C high-density lipoprotein cholesterol - CHD coronary heart disease - FH familial hypercholesterolemia - HMG CoA hydroxy-3methyl-glutaryl coenzyme A - PTT partial thromboplastin time - IU international units - ANOVA analysis of variance