家族性高胆固醇血症患者二例的LDLR基因复合杂合新突变分析

目的 探讨2例临床确诊的湖北籍FH患者的LDLR基因突变状况,为FH的基因诊断提供依据.方法 收集2例临床确诊的FH患者及其父母血脂检测指标等临床资料,通过PCR扩增LDLR基因的1～18个外显子和内含子区域,再将扩增产物进行正、反双向核苷酸序列分析,并与GenBank中LDLR基因的正常序列对比找出突变后,结合FH先证者的临床表型证实致病突变的类型.结果 氧化酶法测定1号、2号FH先证者血浆TC,分别为12.79、11.98 mmol/L;经核苷酸序列分析,其ApoB100基因涵盖的3 500～3 531区域均未见突变;LDLR基因均为复合杂合突变,1号FH先证者LDLR基因第4外显子的665位碱基G>T为杂合错义突变,且该突变为新的点突变,第9内含子的1 358+32位碱基C>T突变也为新的点突变,并均由其父母遗传.2号先证者第9外显子1 257位碱基C>A突变导致终止密码子提前出现,但其核苷酸改变与比利时报道的C>G不同,第13外显子检测到1 879位碱基G>A杂合错义突变,且分别来源于其父母.结论 2例FH先证者均存在LDLR基因复合杂合突变,1号FH先证者的第4外显子665位碱基G>T和第9内含子1 358+32位碱基C>T、2号FH先证者的第9外显子1 257位碱基C>A突变均为新突变,这可能是导致FH的分子机制.

Abstract：

Objective To determine LDLR gene mutation in 2 clinically diagnosed FH patients from Hubei province and provide basis for gene diagnosis of FH.Methods Clinical data of 2 FH patients and their parents were collected.The promoter region and exon 1 to exon 18 region of LDLR gene were amplified through PCR and the amplified products were analyzed by forward and reverse DNA sequencing.The mutations were identified after comparison with LDLR gene sequence in GenBank.The pathogenic gene mutations were confirmed according to both genotype and phenotype of FH probands.Results The levels of plasma TC of two probands were 12.79 and 11.98 mmol/L.respectively.No gene mutations were detected in region 3 500 to 3 531 of ApoB100. The mutations of LDLR gene were compound heterozygous mutations. The novel mutation 665G > T detected in the exon 4 of No. 1 proband's LDLR gene was heterozygous missense mutation. The novel mutation 1 358 +32C > T was detected in the exon 9 of No. 1 proband's LDLR gene.The mutations 665G > T ( paternal origin) and 1 358 + 32C > T ( maternal origin) were inherited from the parents. A novel mutation 1 257 C > A was detected in the exon 9 of No. 2 proband's LDLR gene, resulting the presence of a premature termination codon, which was different from 1 257 C > G reported in Belgium.Another heterozygous missense mutation 1 879 G > A was detected in exon 13. They were derived from paternal origin and maternal origin, respectively. Conclusions There are three novel gene mutations:665G >T, 1 358 +32C > T, 1 257C > A found in two probands with compound heterozygous mutations in LDLR respectively. They maybe play a potential role in FH pathogensis.     

一个纯合家族性高胆固醇血症家系低密度脂蛋白受体基因突变的检测

目的 检测家族性高胆固醇血症(familial hypercholestero-lemia,FH)患者低密度脂蛋白受体(low density lipoprotein receptor,LDLR)的基因突变.方法 提取家系中,临床通过典型特征和血脂检测诊断为家族性高胆固醇血症患者的基因组DNA,首先检测载脂蛋白B100(apoB100)基因R3500Q突变,以排除家族性apoB100缺陷症(Familial defective apoB100,FDB).然后用降落聚合酶链反应(TOUCH-DOWN PCR)扩增该基因的启动子和全部18个外显子,再用单链构象多态性(SSCP)方法分析PCR产物,并对电泳结果异常者进行DNA测序分析.用ANTHEPROT 5.0软件对突变LDLR进行二级结构分析,然后对突变LDLR进行SWISS MODEL在线三级结构预测.结果 通过SSCP和DNA测序发现该家系患者13号外显子存在A606T的纯合突变,采用ANTHEPROT5.0软件的GORⅠ法对突变型和野生型蛋白质进行二级结构分析,可见突变蛋白的突变区域部分螺旋结构被转角结构和无规卷曲取代,其二级结构发生了改变.突变LDLR三级结构预测未发现主链结构的变化.结论 结果表明.LDLR基因A606T的突变可能是此高胆固醇血症家系的致病原因所在.     

Detection of a novel exon 4 low-density lipoprotein receptor gene deletion in a swiss family with severe familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is an autosomal dominant disease which results in 2-3-fold elevated cholesterol levels and in accelerated atherosclerosis. FH is caused by small mutations or larger rearrangements in the low-density lipoprotein receptor (LDLR). Here, we report that screening the LDLR gene in a Swiss family (n = 15) with clinical symptoms of FH by combined single strand conformation polymorphism and long-distance PCR identified a novel 1.3 kb deletion in the LDLR. The deletion eliminated exon 4 of the LDLR presumably by recombination between two identical 25 bp repeats present in intron 3 and 4. The 25 bp sequence in intron 3 is part of an Alu repeat, whereas no homology to Alu repeats was found for the intron 4 region. This 1.3 kb LDLR deletion allele cosegregated with elevated cholesterol levels over three generations. Even on high-dose statin therapy, carriers of the deletion averaged 1.6 times higher cholesterol levels and 1.9 times higher apolipoprotein B-100 (apoB-100) levels than non-carriers who had lipid and apoB-100 levels within the range of the Swiss population. Most affected members of the first and second generation of this family had experienced a first myocardial infarction (MI) before the age of 55 years and most LDLR gene deletion carriers older than 40 years showed severe coronary artery disease (CAD). Hence, we conclude that deletion of exon 4 in the LDLR gene drastically decreases low-density lipoprotein binding leading to severe hypercholesterolemia.     

Two common low density lipoprotein receptor gene mutations cause familial hypercholesterolemia in Afrikaners.

Familial hypercholesterolemia (FH), an autosomal dominant disease caused by mutations in the LDL receptor gene, is five times more frequent in the Afrikaner population of South Africa than it is in the population of the United States and Europe. It has been proposed that the high frequency is due to a founder effect. In this paper, we characterized 24 mutant LDL receptor alleles from 12 Afrikaner individuals homozygous for FH. We identified two mutations that together makeup greater than 95% of the mutant LDL receptor genes represented in our sample. Both mutations were basepair substitutions that result in single-amino acid changes. Each mutation can be detected readily with the polymerase chain reaction and restriction analysis. The finding of two common LDL receptor mutations in the Afrikaner FH homozygotes predicts that these mutations will predominate in the Afrikaner population and that the high frequency of FH is due to a founder effect. The increased incidence of ischemic heart disease in the Afrikaner population may in part be due to the high frequency of these two mutations in the LDL receptor gene.     

Effects of atorvastatin and simvastatin on low-density lipoprotein subfraction profile, low-density lipoprotein oxidizability, and antibodies to oxidized low-density lipoprotein in relation to carotid intima media thickness in familial hypercholesterolemia.

BACKGROUND: Little is known about the effects of statins on the quality of circulating low-density lipoprotein (LDL) in relation to atherosclerosis progression. METHODS: In a double-blind, randomized trial of 325 patients with familial hypercholesterolemia (FH), we assessed the effects of high-dose atorvastatin (80 mg) and conventional-dose simvastatin (40 mg) on LDL subfraction profile (n = 289), LDL oxidizability (n = 121), and circulating autoantibodies to oxidized LDL (n = 220). Progression of atherosclerosis was measured by carotid intima media thickness (IMT) (n = 325). RESULTS: At baseline, the patients showed an intermediate LDL subfraction profile composed of three LDL subfractions (LDL1, LDL2, LDL3), with LDL2 as the predominant subfraction. A strong negative correlation was found between plasma triglycerides and the LDL subfraction profile (r = -.64, p = .000). Both plasma levels of triglycerides and small dense LDL3 correlated weakly with baseline IMT (r = .11, p = .04 and r = .15, p = .01, respectively; n = 289). No association was found between baseline IMT and oxidation parameters or circulating antibodies to oxidized LDL. Atorvastatin reduced triglycerides, LDL cholesterol, and all LDL subfractions to a greater extent than did simvastatin and led to regression of carotid IMT. However, LDL subfraction pattern and plasma levels of autoantibodies to oxidized LDL remained unchanged in both treatment groups, and LDL oxidizability increased minimally to a similar extent in both groups. Significant treatment differences were found for the rate of in vitro oxidation of LDL and the amount of dienes formed during in vitro oxidation of LDL, which both decreased more following atorvastatin than after simvastatin. CONCLUSION: Change of IMT after statin treatment was associated with baseline IMT (r = .41), LDL cholesterol (r = -.20), and the amount of dienes formed during in vitro oxidation of LOL (r = .28) but not with plasma levels of antibodies to oxidized LDL, in vitro LDL oxidizability, and LDL subfraction profile.     

1例家族性高胆固醇血症患者低密度脂蛋白受体基因新突变体功能研究

目的分析基因突变对低密度脂蛋白受体(LDLR)功能的影响,探讨其对家族性高胆固醇血症(FH)的可能致病机制。方法对1名FH患者进行基因检测,构建真核细胞表达载体,经定点诱变获得突变受体质粒,并将突变受体质粒转染入人胚肾(HEK293)细胞中,用激光共聚焦显微镜(CLSM)观察突变蛋白细胞定位,用流式细胞术检测突变蛋白表达及内吞活性变化。结果基因测序显示该名患者发生了LDLR基因Y398X突变;CLSM结果显示突变蛋白部分滞留于内质网中;流式细胞术结果显示细胞表面LDLR表达量减少至5.5%,内吞活性减少至20.1%。结论在临床确诊的FH患者中检测到LDLR致病性基因Y398X突变,在中国为首次报道。该突变造成LDLR转运缺陷,从而导致血浆中胆固醇代谢障碍,继而诱发FH的发生。     

羊水细胞低密度脂蛋白受体基因突变分析在家族性高胆固醇血症产前诊断中应用

目的探讨羊水细胞低密度脂蛋白受体（low density lipoprotein receptor,LDLR）基因突变分析在家族性高胆固醇血症（familial hypercholesterolemia,FH）产前诊断中的应用价值。方法 3例曾生育FH重症患儿并再次妊娠的妇女及其核心家系成员,提取其外周血基因组DNA,筛查LDLR基因突变;于妊娠16～20周在超声引导下行羊膜腔穿刺术抽取羊水,提取胎儿脱落细胞DNA,分别对家系存在的LDLR基因突变进行检测,判断胎儿是否为重症FH。结果 3个家系均符合FH诊断,并分别在LDLR基因检测到2个互不相同的杂合突变位点;胎儿LDLR基因核苷酸序列分析证实,1号家系胎儿仅携带该家系1个突变位点判断为杂合（轻症）,2号家系胎儿携带该家系2个突变位点判断为复合杂合（重症）,3号家系胎儿未检到该家系的突变位点推测为正常个体。结论 FH孕妇羊水脱落细胞LDLR基因分析安全有效,可尽早发现FH纯合子患儿。     

Decrease of thyroid hormones in patients with familial hypercholesterolemia during dextran sulphate low-density lipoprotein apheresis

Removal of low-density lipoproteins from plasma by dextran sulfate adsorption (DSA) in FH patients entails a decrease in plasma levels of thyroid hormones (?28.5% and ?18.7%, respectively, for T3 and T4). This suggests that FH patients have a greater than normal fraction of thyroid hormones bound to lipoproteins, due to their expanded lipoprotein pool.     

Association of coronary artery ectasia with plasma insulin levels in Japanese men of heterozygous familial hypercholesterolemia with the low-density lipoprotein receptor gene mutation K790X

BACKGROUND: Hyperinsulinemia is widely believed to be an important coronary risk factor. We investigated the effect of plasma insulin levels on the development of coronary ectasia in Japanese men with heterozygous familial hypercholesterolemia (FH). METHODS: A cross-sectional study was conducted in 20 FH men with the LDL receptor mutation (K790X) [age 42.3+/-2.8 years old, body mass index (BMI) 24.6+/-0.7 kg/m2, total cholesterol (TC) 8.68+/-0.36 mmol/l, triglycerides (TG) 1.76+/-0.23 mmol/l, high-density lipoprotein cholesterol (HDL-C) 0.977+/-0.065 mmol/l]. Subjects with diabetes mellitus were excluded. Plasma insulin levels, either fasting or during oral glucose tolerance test, were compared between subjects with and without coronary artery ectasia. RESULTS: FH subjects with coronary ectasia had significantly higher fasting plasma insulin levels than those without (12.6+/-1.4 vs. 7.7+/-0.5 mU/l; p<0.05). Also, plasma insulin levels during oral glucose tolerance test tended to be higher in the former than in the latter. CONCLUSIONS: Plasma insulin level could be an important determinant of the development of coronary artery ectasia in Japanese heterozygous FH men.     

Is responsiveness to lovastatin in familial hypercholesterolaemia heterozygotes influenced by the specific mutation in the low-density lipoprotein receptor gene?

Abstract. Lovastatin is one of the most commonly used lipid-lowering drugs in familial hypercholesterolaemia (FH) heterozygotes. In order to study whether the response to lovastatin is influenced by the underlying mutation in the low-density lipoprotein (LDL) receptor gene, the authors compared the response in 24 heterozygotes in whom the mutation has been classified and in 34 heterozygotes in whom the mutation has not been classified. Those possessing a classified mutation had significantly higher pre-trial values of LDL-cholesterol than those possessing an unclassified mutation. However, no difference was found in the response to lovastatin. Nor were there any differences in the response between subjects possessing one of the three different classified mutations. Furthermore, irrespective of whether or not the mutation had been classified, no difference in the response was found between subjects in the upper and lower quartile with respect to pre-trial values of LDL-cholesterol. The authors conclude that the response to lovastatin is independent of both the specific mutation in the LDL receptor gene and the actual cholesterol level in FH heterozygotes.     

The familial hypercholesterolemia regression study: a randomized comparison of therapeutic reduction of both low-density lipoprotein and lipoprotein(a) versus low-density lipoprotein alone.

Lipoprotein (a) [Lp (a)] is a risk factor for coronary heart disease (CHD), especially in the presence of a raised low-density lipoprotein (LDL)-cholesterol (LDL-C). To ascertain whether reduction of both LDL and Lp(a) is more advantageous than reduction of LDL alone, patients with heterozygous FH and CHD were selected randomly to receive either LDL apheresis fortnightly plus simvastatin 40 mg/day or colestipol 20 g plus simvastatin 40 mg/day. Quantitative coronary angiography was undertaken before and after 2.1 years. Changes in serum lipids were similar in both groups except for the greater reduction of LDL-C and Lp(a) by apheresis. There were no significant differences in primary angiographic endpoints, and none of the angiographic changes correlated with Lp(a). Although LDL apheresis plus simvastatin was more effective than colestipol plus simvastatin in reducing LDL-C and Lp(a), it was not more beneficial in influencing coronary atherosclerosis. Decreasing Lp(a) seems unnecessary if LDL-C is reduced below 130 mg/dl.     

The effect of combined fenofibrate and cholestyramine therapy on low-density lipoprotein kinetics in familial hypercholesterolemia patients

The effects of combined drug treatment (fenofibrate and cholestyramine) have been investigated in vivo by simultaneously determining total and receptor-independent LDL catabolism with 125I-labelled LDL and 131I-labelled LDL coupled with cyclohexanedione. Receptor-mediated catabolism of LDL determined as the difference between the turnover of 125I and 131I, was found to be reduced in heterozygotes with familial hypercholesterolemia. Treatment with combined fenofibrate and cholestyramine markedly stimulated both receptor-mediated (by more than 2-fold) and receptor-independent catabolism. LDL-Apo B and LDL-cholesterol levels were reduced by 38% and 36%, respectively. The combined treatment also reduced the absolute synthetic rate of LDL-Apo B (by 9%). The mechanisms responsible for these kinetic effects are discussed.     

单链构象多态性技术在家族性高胆固醇血症患者低密度脂蛋白受体基因13外显子点突变筛查中的应用

目的 探讨单链构象多态性(SSCP)技术在家族性高胆固醇血症患者低密度脂蛋白受体(LDLR)基因13外显子点突变筛查上的应用价值.方法 以16例临床诊断为家族性高胆固醇血症(FH)患者为研究对象,提取外周血DNA,扩增LDLR基因第13号外显子片段,组合最优条件进行SSCP电泳并银染.对异常条带进行DNA序列测定确定其突变性质和位置.结果 优化SSCP电泳条件为:不含甘油8%凝胶,在10℃条件下电泳;含5%甘油的8%凝胶,在常温条件下电泳(交联度均为49:1).凝胶厚度均不超过0.4 mm,电泳电压为5 V/cm,在此条件下进行SSCP电泳均可以得到满意电泳图谱.对发现的异常条带,结合DNA测序证实有4例患者LDLR基因第13外显子分别发生A606T,D601N,Y601D,或G636V错义突变,同时均存在1959碱基C→T同义突变.另外4例患者13外显子仅存在1959碱基C→T同义突变.结论 通过优化各种条件进行的PCR-SSCP银染方法,是高胆固醇血症病LDLR基因13外显子点突变初步筛查的有效手段.     

Construction and in vitro functional evaluation of a low-density lipoprotein receptor/transferrin fusion protein as a therapeutic tool for familial hypercholesterolemia.

A cDNA sequence encoding a soluble form of the human low-density lipoprotein receptor (LDL-R) was produced by RT-PCR amplification. This form of the receptor contains the N-terminal cysteine-rich domain, the EGF homology domain, and the serine/threonine-rich domain, but lacks the membrane anchor as well as the cytoplasmic domain. By the same technical approach a cDNA sequence encoding rabbit transferrin was generated. In-frame fusion of the two cDNAs produced a sequence encoding a chimeric protein potentially capable of binding LDL on the N-terminal side and the transferrin receptor on the C-terminal side. It was expected that LDL bound to the chimeric protein could be internalized, targeted to an acidic compartment, and processed through the pathway of the transferrin receptor. Cells transfected with the LDL-R/transferrin cDNA translate, glycosylate, and secrete the corresponding protein in the culture medium. The secreted protein binds LDL in a ligand-blotting experiment. Finally, the chimeric protein mediates the binding and internalization of LDL in mutant cells lacking the LDL receptor. In fact, Watanabe rabbit fibroblasts, incubated with the chimeric protein show a fourfold increase in LDL binding, a fivefold increase in LDL internalization, and a sixfold increase in LDL degradation, with respect to unincubated fibroblasts.     

Low-density lipoprotein receptor gene therapy using helper-dependent adenovirus produces long-term protection against atherosclerosis in a mouse model of familial hypercholesterolemia

We tested the efficacy of low-density lipoprotein receptor (LDLR) therapy using helper-dependent adenovirus (HD-Ad), comparing it with that of very low-density lipoprotein receptor (VLDLR), an LDLR homolog. We treated high cholesterol diet fed LDLR-/- mice with a single intravenous injection of HD-Ad expressing monkey LDLR (1.5 x 10(13) or 5 x 10(12) VP/kg) or VLDLR. Throughout the 24-week experiment, plasma cholesterol of LDLR-treated mice was lower than that of VLDLR-treated mice, which was in turn lower than that of PBS-treated mice. Anti-LDLR antibodies developed in 2/10 mice treated with high-dose HD-Ad-LDLR but in none (0/14) of the other treatment groups. HD-Ad-treated mice displayed significant retardation of atherosclerotic lesion progression. We next tested the long-term efficacy of low-dose HD-Ad-LDLR injected into 12-week-old LDLR-/- mice. After 60 weeks, atherosclerosis lesions covered approximately 50% of the surface of aortas of control mice, whereas aortas of treated mice were essentially lesion-free. The lipid lowering effect of HD-Ad-LDLR lasted at least 108 weeks (>2 years) when all control mice had died. In addition to retarding lesion progression, treatment caused lesion remodeling from a vulnerable-looking to a more stable-appearing phenotype. In conclusion, HD-Ad-mediated LDLR gene therapy is effective in conferring long-term protection against atherosclerosis in a mouse model of familial hypercholesterolemia.     

Serum noncholesterol sterols related to cholesterol metabolism in familial hypercholesterolemia

Serum cholesterol precursor levels and plant sterol were related to parameters of cholesterol metabolism in 22 patients with heterozygous familial hypercholesterolemia. The serum levels of cholesterol precursor sterols were inversely related to fractional absorption of dietary cholesterol and subsequently positively to overall cholesterol synthesis. The serum plant sterol levels, on the contrary, were significantly associated with fractional cholesterol absorption and negatively with overall cholesterol synthesis. These results were confirmed also with multivariate analyses. Fecal lanosterol, a cholesterol precursor, was related positively to cholesterol synthesis measured by sterol balance and serum precursors and negatively to serum plant sterols. The serum precursor and plant sterol levels were inversely significantly related to each other, indicating that the higher cholesterol absorption efficiency the higher are the serum plant sterol levels and the lower the precursor sterol contents and the overall cholesterol synthesis.     

Demonstration of functional low-density lipoprotein receptors by protein blotting in fibroblasts from a subject with homozygous receptor-negative familial hypercholesterolemia

We report the detection of low-density lipoprotein (LDL) receptors by the technique of receptor blotting in fibroblasts from a patient with homozygous familial hypercholesterolemia (FHC) previously classified as "receptor negative." Solubilized receptors were electrophoresed, transferred to nitrocellulose paper, treated with LDL followed by radiolabeled antibody to LDL, and visualized by autoradiography. GM 2000 FHC fibroblasts revealed LDL receptors with an apparent molecular weight of approximately 140,000, the same as in normal cells. LDL receptor activity by blotting in GM 2000 cells was greatly diminished in comparison with normal cells, but was calcium dependent. Receptor activity was also detectable by conventional monolayer binding and degradation assays. Thus, GM 2000 cells have profoundly diminished LDL receptor activity, but retain the genetic capacity to make LDL receptor material of normal molecular weight that is capable of binding LDL. Previous studies have demonstrated the presence of trace amounts of immunoreactive LDL receptor protein in fibroblasts from some receptor-negative FHC homozygotes. Our work extends these studies by demonstrating the ability of this material to bind LDL.