Familial Hypercholesterolemia Homozygotes Research Articles

ANGPTL3 Downregulation Increases Intracellular Lipids by Reducing Energy Utilization.

ANGPTL3 (angiopoietin-like protein 3) is a circulating protein with a key role in maintaining lipoprotein homeostasis. A monoclonal antibody against ANGPTL3 is an approved and well-tolerated treatment to reduce lipoproteins in familial hypercholesterolemia homozygotes. However, the reduction of hepatic ANGPTL3 synthesis using an antisense oligonucleotide unexpectedly resulted in a dose-dependent increase in liver lipid content and circulating transaminases, resulting in the termination of the clinical trial. Meanwhile, the use of silencing RNAs remains an area of active investigation. Our study sought to investigate whether intracellular downregulation of ANGPTL3 may lead to a primary increase in neutral lipids within the hepatocyte. We downregulated ANGPTL3 by silencing RNA in primary human hepatocytes 3-dimensional spheroids, HepG2/LX-2 3-dimensional spheroids, and in HepG2, Hep3B2, and Huh7 cultured in 2 dimensions. ANGPTL3 downregulation increased neutral lipids in all models investigated. Interestingly, ANGPTL3 induced lower intracellular deiodinase type 1 protein levels resulting in a reduction in beta-oxidation and causing an increase in triglycerides stored in lipid droplets. In conclusion, intracellular ANGPTL3 downregulation by silencing RNA led to an increase in triglycerides content due to a reduction in energy substrate utilization resembling a primary intracellular hepatocyte hypothyroidism.

Use of apheresis in the age of new therapies for familial hypercholesterolaemia.

Lipoprotein apheresis has been first line therapy for homozygous familial hypercholesterolaemia (FH) and other severe and refractory forms of dyslpidaemia for over 40 years but the recent advent of novel and potent LDL-lowering compounds necessitates a reappraisal of its role. During the past decade a substantial amount of evidence has accumulated describing the effect of LDL-lowering with apheresis and conventional drug therapy upon the cardiovascular outcomes associated with homozygous and statin-refractory heterozygous FH. This has necessitated re-defining the target levels of LDL cholesterol needed to arrest progression of atherosclerosis in these situations. At the same time, evidence has accrued regarding the pathogenicity of raised levels of lipoprotein (a) and the promising role of apheresis in mitigating the adverse effects of the latter. The latest advance in treatment has been the introduction of three classes of novel and potent LDL-lowering compounds in the shape of inhibitors of Propertin convertase subtilisin kexin 9 (PCSK9), microsomal triglyceride transfer protein and angiopoietin-like 3. These recent developments raise the question of whether these compounds will be used as adjuvants to bolster lipoprotein apheresis in FH homozygotes or whether they will render it obsolete, as is already occurring with PCSK9 inhibitors in FH heterozygotes.

Effectiveness and Safety of Lipid-Lowering Drug Treatments in Japanese Patients with Familial Hypercholesterolemia: Familial Hypercholesterolemia Expert Forum (FAME) Study.

Aims: Familial hypercholesterolemia (FH) is a genetic disorder characterized by high serum levels of low-density lipoprotein (LDL)-cholesterol (LDL-C), tendon and skin xanthomas, and premature coronary artery disease (CAD). In Japan, detailed information on the current status of drug therapies for patients with FH has not been reported so far, and their efficacy and safety have not been clarified. After the introduction of ezetimibe, which can further reduce serum LDL-C levels on top of statins, the changes of management for FH patients with these drugs are of particular interest. The current study aimed to evaluate the clinical status of FH heterozygotes and homozygotes, especially focusing on the real-world lipid-lowering drug therapy, attained serum LDL-C levels, and cardiovascular events at registration and during the follow-up. Methods: The FAME Study enrolled 762 heterozygous (including 17 newly diagnosed cases) and 7 homozygous FH patients from hospitals and clinics nationwide. Diagnosis of FH was based upon the criteria defined in the Study Report in 2008 of the Research Committee on Primary Hyperlipidemia supported by Grants-in-Aid for Scientific Research from the Japanese Ministry of Health, Labor and Welfare. Data analysis was primarily carried on heterozygous FH patients. Results: Xanthoma or thickening of the Achilles tendon was observed in more than 80% of the patients. CAD was recorded in 23% of patients. Patients with parental and sibling CAD accounted for 47% and 24%, respectively. At baseline, patients without CAD who had LDL-C ＜100 mg/dL accounted for 12.3% and those with CAD who had attained the target (LDL-C ＜70 mg/dL) in the secondary prevention accounted for only 1.8%. In the multiple logistic analysis, male sex, age ＞40, heterozygous FH score ＞20, hypertension, and sibling CAD were significantly and positively associated with prevalent CAD, whereas serum HDL-cholesterol levels showed a significant inverse association with CAD. Patients treated with statin alone, statin＋ezetimibe, statin＋resin, or statin＋probucol accounted for 31.1%, 26.3%, 4.0%, and 3.7%, respectively. Patients treated with three-drug combination (statin＋ezetimibe＋resin or statin＋ezetimibe＋probucol) accounted for 7.5%. Statins and ezetimibe were used in 88.0% and 48.0% at the baseline, respectively. Although high-intensity statins were mainly prescribed, statin doses were much lower than those reported in Western countries. The addition of ezetimibe resulted in ~20% reduction in serum LDL-C. CAD was diagnosed in 17 patients with 21 episodes during follow-up. The Cox hazard model analysis demonstrated that male sex, CAD at the baseline, and parental CAD were related to the development of atherosclerotic cardiovascular disease (ASCVD) events. Furthermore, an increase in serum HDL-C was associated with a significant reduction of ASCVD events, while serum LDL-C and triglyceride levels were not related to ASCVD events. Conclusion: The prevalence of CAD in Japanese patients with heterozygous FH is still very high. In most of the cases, the target level of serum LDL-C was not achieved for primary and secondary prevention of CAD, suggesting that a more aggressive LDL-C lowering and appropriate management of residual risks are necessary.

Guidelines for Diagnosis and Treatment of Familial Hypercholesterolemia 2017.

StatementFamilial hypercholesterolemia (FH) is an autosomal hereditary disease with the 3 major clinical features of hyper-LDL-cholesterolemia, premature coronary artery disease and tendon and skin xanthomas. As there is a considerably high risk of coronary artery disease (CAD), in addition to early diagnosis and intensive treatment, family screening (cascade screening) is required (Recommendation level A)For a diagnosis of FH, at least 2 of the following criteria should be satisfied:① LDL-C ≥ 180 mg/dL, ② Tendon/skin xanthomas, ③ History of FH or premature CAD within 2nd degree blood relatives (Recommendation level A)Intensive lipid-lowering therapy is necessary for the treatment of FH. First-line drug should be statins. (Recommendation level A, Evidence level 3)Screening for CAD as well as asymptomatic atherosclerosis should be conducted periodically in FH patients. (Recommendation level A)For homozygous FH, consider LDL apheresis and treatment with PCSK9 inhibitors or MTP inhibitors. (Recommendation level A)For severe forms of heterozygous FH who have resistant to drug therapy, consider PCSK9 inhibitors and LDL apheresis. (Recommendation level A)Refer FH homozygotes as well as heterozygotes who are resistant to drug therapy, who are children or are pregnant or have the desire to bear children to a specialist. (Recommendation level A)

Survival in homozygous familial hypercholesterolaemia is determined by the on-treatment level of serum cholesterol.

Homozygous familial hypercholesterolaemia (FH) is a rare inherited disorder characterized by extreme hypercholesterolaemia from birth, accelerated atherosclerosis, and premature death. Many forms of lipid-lowering therapies have been used in the past, but definitive evidence of benefit has been lacking. We therefore undertook a retrospective survey of lipid levels and clinical outcomes of FH homozygotes treated with a combination of lipid-lowering measures between 1990 and 2014 in South Africa and the UK. We divided 133 previously statin-naive homozygotes into quartiles according to their on-treatment levels of serum cholesterol and compared the occurrence of any death, cardiovascular death, and major adverse cardiovascular events (MACE) between the quartiles during 25 years of follow-up, using Cox and competing risks regression analysis. Patients in Quartile 4, with an on-treatment serum cholesterol >15.1 mmol/L, had a hazard ratio of 11.5 for any death compared with those in Quartile 1, with an on-treatment cholesterol of < 8.1 mmol/L. Those in Quartiles 2 and 3 combined, with on-treatment cholesterol of 8.1-15.1 mmol/L had a hazard ratio of 3.6 compared with Quartile 1. These differences were statistically significant (P < 0.001) and remained so after adjustments for confounding factors (P = 0.04). Significant differences between quartiles were also evident for cardiovascular deaths and MACE. These findings provide unequivocal evidence that the extent of reduction of serum cholesterol achieved by a combination of therapeutic measures, including statins, ezetimibe, lipoprotein apheresis, and evolocumab, is a major determinant of survival in homozygous FH.

The elevation of plasma concentrations of apoB-48-containing lipoproteins in familial hypercholesterolemia is independent of PCSK9 levels

BackgroundPrevious studies have reported high plasma concentrations of both intestinal apolipoprotein (apo) B-48-containing lipoproteins and PCSK9 in subjects with familial hypercholesterolemia (FH). However, the extent to which LDL receptor deficiency and PCSK9 levels influence plasma apoB-48 concentrations in humans remains to be fully characterized. The objective of the study was to assess the independent association between FH, PCSK9 concentrations and plasma apoB-48 levels in a large cohort of genetically defined FH heterozygotes (HeFH) and homozygotes (HoFH).MethodsA total of 118 HeFH, 6 HoFH, and 117 controls were included in the study. Plasma PCSK9 and apoB-48 concentrations were measured in the fasting state.ResultsPlasma PCSK9 and apoB-48 levels were higher in FH subjects compared with controls (PCSK9: HoFH: 642.6 ± 246.9 vs. HeFH: 324.9 ± 119.8 vs. controls: 194.5 ± 65.9 ng/mL, P < 0.0001; apoB-48: HoFH: 14.71 ± 4.36 vs. HeFH: 6.55 ± 4.24 vs. controls: 3.03 ± 2.07 μg/mL; P < 0.0001). There were no correlations between apoB-48 and PCSK9 plasma levels in both controls (ρ = 0.06, P = 0.5) and HeFH subjects (ρ = 0.07, P = 0.4). Multiple linear regression analysis showed that the FH status was the only independent factor associated with apoB-48 levels, contributing to 28.7% of the variance (P < 0.0001).ConclusionsThese data indicate that the elevation in plasma apoB-48 levels associated with FH is independent of PCSK9 levels.Trial registrationNCT02225340.

Improved cardiovascular outcomes following temporal advances in lipid-lowering therapy in a genetically-characterised cohort of familial hypercholesterolaemia homozygotes

There is a paucity of data concerning the influence of lipid-lowering therapy on cardiovascular (CV) outcomes in patients with homozygous familial hypercholesterolaemia (FH). To redress this a retrospective analysis was undertaken of the demographic features, lipid levels, low density lipoprotein receptor and Autosomal Recessive Hypercholesterolaemia gene mutations, CV outcomes and vital status of 44 FH homozygotes referred to a single centre in the UK between 1964 and 2014. Data were obtained from past publications, case records and death certificates. Differences in categorical and continuous variables between living and dead patients were analysed using Fisher's exact test and an independent t-test respectively. During the 50 years covered by this survey 13 patients have died, 30 are still alive and 1 was lost to follow up. The mean age of Alive patients was 32.6 ± 11.5 versus 28.3 ± 14.9 years in Dead ones (P = 0.31) and they were born 18 years later (P = 0.0001). Pre-treatment serum total cholesterol (TC) was similar in Alive and Dead (20.2 ± 5.1 v 21.3 ± 4.4 mmol/l, P = 0.52) but on-treatment TC was lower in Alive than Dead (8.1 ± 2.8 v 14.5 ± 6.0 mmol/l, P = 0.0001) and CV adverse events were far less frequent (eg aortic stenosis, 33% v 77%, P = 0.02). The lower on-treatment TC and fewer CV adverse events in FH homozygotes still living reflect advances in apheresis and drug therapy since the 1990s. Further improvements in prognosis can be expected with the impending introduction of novel lipid-lowering agents.

Removal of plasma mature and furin-cleaved proprotein convertase subtilisin/kexin 9 by low-density lipoprotein-apheresis in familial hypercholesterolemia: development and application of a new assay for PCSK9.

Proprotein convertase subtilisin/kexin 9 (PCSK9) is known to be a good target to decrease LDL cholesterol (LDL-C) and two forms of PCSK9, mature and furin-cleaved PCSK9, circulate in blood. However, it has not been clarified whether and how the levels of each PCSK9 are affected by LDL-apheresis (LDL-A) treatment, a standard therapy in patients with severe forms of familial hypercholesterolemia (FH). Our objective was to investigate the differences in LDL-A-induced reduction of mature and furin-cleaved PCSK9 between homozygous and heterozygous FH, and between dextran sulfate (DS) cellulose adsorption and double membrane (DM) columns and to clarify the mechanism of their removal. A sandwich ELISA to measure two forms of PCSK9s using monoclonal antibodies was developed. Using the ELISA, PCSK9 levels were quantified before and after LDL-A with DS columns in 7 homozygous and 11 heterozygous FH patients. A crossover study between the two column types was performed. The profiles of PCSK9s were analyzed after fractionation by gel filtration chromatography. Immunoprecipitation of apolipoprotein B (apoB) in FH plasma was performed. Both mature and furin-cleaved PCSK9s were significantly decreased by 55-56% in FH homozygotes after a single LDL-A treatment with DS columns, and by 46-48% or 48-56% in FH heterozygotes after treatment with DS or DM columns. The reduction ratios of LDL-C were strongly correlated with that of PCSK9 in both FH homozygotes and heterozygotes. In addition, more than 80% of plasma PCSK9s were in the apoB-deficient fraction and a significant portion of mature PCSK9 was bound to apoB, as shown by immunoprecipitation. Both mature and furin-cleaved PCSK9s were removed by LDL-A in homozygous and heterozygous FH either by binding to apoB or by other mechanisms. The ELISA method to measure both forms of plasma PCSK9 would be useful for investigating physiological or pathological roles of PCSK9.

The history of Autosomal Recessive Hypercholesterolemia (ARH). From clinical observations to gene identification

The most frequent form of monogenic hypercholesterolemia, also known as Familial Hypercholesterolemia (FH), is characterized by plasma accumulation of cholesterol transported in Low Density Lipoproteins (LDLs). FH has a co-dominant transmission with a gene-dosage effect. FH heterozygotes have levels of plasma LDL-cholesterol (LDL-C) twice normal and present xanthomas and coronary heart disease (CHD) in adulthood. In rare FH homozygotes plasma LDL-C level is four times normal, while xanthomas and CHD are present from infancy. Most FH patients are carriers of mutations of the LDL receptor (LDLR); a minority of them carry either mutations in the Apolipoprotein B (ApoB), the protein constituent of LDLs which is the ligand for LDLR, or gain of function mutations of PCSK9, the protein responsible for the intracellular degradation of the LDLR. From 1970 to the mid 90s some publications described children with the clinical features of homozygous FH, who were born from normocholesterolemic parents, strongly suggesting a recessive transmission of FH. In these patients the involvement of LDLR and APOB genes was excluded. Interestingly, several patients were identified in the island of Sardinia (Italy), whose population has a peculiar genetic background due to geographical isolation. In this review, starting from the early descriptions of patients with putative recessive hypercholesterolemia, we highlight the milestones that led to the identification of a novel gene involved in LDL metabolism and the characterization of its encoded protein. The latter turned out to be an adaptor protein required for the LDLR-mediated endocytosis of LDLs in hepatocytes. The loss of function of this protein is the cause of Autosomal Recessive Hypercholesterolemia (ARH).

Pharmacological treatment of a Sardinian patient affected by Autosomal Recessive Hypercholesterolemia (ARH)

Previous studies have shown that patients with autosomal recessive hypercholesterolemia (ARH) resulting from mutations in LDLRAP1 gene have a less severe cardiovascular involvement than familial hypercholesterolemia homozygotes, lower levels of low-density lipoprotein cholesterol (LDL-C), and higher levels of high-density lipoprotein cholesterol (HDL-C). In addition, ARH patients seem to be more responsive to the lipid-lowering drugs. The aim was to test the effect of a combined drug treatment in an ARH patient in the absence of plasmapheresis. Here we report the lipid-lowering effect of rosuvastatin (60mg/day) associated with ezetimibe (10mg/day) in a single ARH patient. The sequencing of LDLRAP1 gene showed that the patient was homozygous for the c.432insA mutation. During a 6-month treatment, we observed an 80% reduction of LDL-C and a significant increase of HDL-C and ApoA-I. Some sequence variations in PCSK9 and NPC1L1 genes found in this patient may have contributed to the success of drug treatment. Our findings, although limited to a single case, suggest that in many ARH patients the LDL-C goal may be reached with the more potent statins associated with ezetimibe in the absence of extracorporeal procedures.

Abstract 18972: A 36-Year-Old Man with Stroke and Severe Hyperlipidemia: From Phenotype to Genotype

A 36-year-old man with a history of hypertension and hyperlipidemia was admitted to the hospital with headaches, a left visual field deficit and a right occipital lobe infarct. Family history is notable for multiple maternal relatives with premature coronary artery disease and severe hyperlipidemia. Laboratory testing revealed an LDL level of 325 mg/dl. Echocardiography demonstrated a bicuspid aortic valve and two highly mobile thrombi at the sinotubular junction. Because there was no aortic false lumen and the clinical picture was most suspicious for a ruptured aortic root atheroma, we administered intravenous heparin with plans for aortic thrombectomy pending his hemodynamics, neurological status and changes in the echocardiographic apperance of the presumed thrombi. On day three, the patient experienced acute chest pain and ST elevation concerning for abrupt occlusion of the right coronary artery. He was taken emergently to the operating room where two thrombi_one of which was lodged in the right coronary ostium_were removed and aortic endarterectomy was performed. Histology of the aortic specimen showed atherosclerosis and inflammation but no evidence of medial degeneration. The histologic evidence of atherosclerosis focused attention on the patient’s personal and family history of severe hypercholesterolemia. To assess for a genetic defect in cholesterol metabolism, we directly sequenced the LDL receptor gene and identified a heterozygous missense mutation associated with familial hypercholesterolemia (FH). Aortic root disease is common in FH homozygotes, but its presence in a heterozygote suggests an additional inherited or acquired risk factor and prompts further investigation. The bicuspid valve raises the possibility of a subclinical aortic condition that may have contributed to this unusual syndrome. This case directly illustrates the consequences of aortic plaque rupture and emphasizes the multidisciplinary clinical approaches that are central to understanding the complex links between genotype and phenotype even in a well-characterized "simple" monogenic disorder.

Elevated serum MMP-9/TIMP-1 ratio in patients with homozygous familial hypercholesterolemia: Effects of LDL-apheresis

Matrix degradation within an atherosclerotic plaque is an important pathogenic factor in atherosclerosis, and is largely modulated by the balance between matrix metalloproteinases (MMPs) and their endogenous inhibitors (i.e., tissue inhibitor of MMPs [TIMPs]). Familial hypercholesterolemia (FH) is a rare inherited disorder associated with premature coronary heart disease. The aim of the present study was to examine MMP-9 and TIMP-1 on plasma and cellular mRNA levels in homozygous FH patients (n=7) compared with age- and sex-matched heterozygous FH patients (n=6), and with healthy subjects (n=7), and to test whether once-weekly LDL-apheresis (three consecutive sessions) of homozygous FH patients show short-term effects on these variables. The main findings were that (i) Compared to healthy control subjects, homozygous FH patients have significantly higher serum levels of MMP-9 and lower levels of TIMP-1, and consequently significantly higher MMP-9/TIMP-1 ratio, potentially reflecting higher MMP-9 activity. (ii) Peripheral blood mononuclear cells (PBMC) isolated from FH homozygotes have significantly higher mRNA levels of MMP-9 compared to cells from heterozygotes. (iii) TNFα-stimulated PBMC from FH homozygotes released borderline-significantly more MMP-9 than cells from heterozygotes and healthy controls. (iv) LDL-apheresis (one day before treatment versus fifteen days later, on the day after the weekly treatment) had no significant short-term effect on any of the MMP-9 and TIMP-1 variables measured in serum and cells. The data may suggest that homozygous FH patients have an enhanced matrix degrading potential as compared with heterozygous FH patients and healthy controls, potentially contributing to the increased cardiovascular risk observed in these patients.

Serum levels of proprotein convertase subtilisin/kexin type 9 in subjects with familial hypercholesterolemia indicate that proprotein convertase subtilisin/kexin type 9 is cleared from plasma by low-density lipoprotein receptor–independent pathways

Secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein receptor (LDLR) at the cell surface and disrupts the normal recycling of the LDLR. When human PCSK9 is injected into LDLR-deficient mice, PCSK9 is still rapidly cleared by the liver. This finding may suggest that PCSK9 is physiologically also cleared by receptors other than the LDLR. An alternative explanation could be that PCSK9 has undergone modifications during purification and is cleared by scavenger receptors on liver endothelial sinusoidal cells when injected into mice. If the only mechanism for clearing PCSK9 in humans is through the LDLR, one would expect that differences in the number of LDLRs would affect the plasma levels of low-density lipoprotein cholesterol (LDLC) and PCSK9 in a similar fashion. In this study, levels of LDLC and PCSK9 were measured in familial hypercholesterolemia (FH) homozygotes, FH heterozygotes, and normocholesterolemic subjects. The ratio between the levels of LDLC and PCSK9 was 1.7-fold higher in FH heterozygotes and 3-fold higher in FH homozygotes than in the normocholesterolemic subjects. Thus, defective LDLRs have a greater impact on the levels of LDLC than on the levels of PCSK9. By assuming that the rate of PCSK9 synthesis is similar in the 3 groups, this finding suggests that in humans, plasma PCSK9 is also cleared by LDLR-independent mechanisms.

The Arabic allele: A single base pair substitution activates a 10-base downstream cryptic splice acceptor site in exon 12 of LDLR and severely decreases LDLR expression in two unrelated Arab families with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a monogenic autosomal dominant disorder caused by defects in LDLR. Few reports describe FH mutations among Arabs. We describe a mutation in LDLR of two unrelated Arab families. We investigated 19 patients using DNA sequencing, RFLP, and real-time (RT) PCR. DNA sequencing showed a base pair substitution (c.1706-2 A>T) in the splice acceptor site of LDLR intron 11. Our results were confirmed by RFLP on 2% agarose gel. In silico analysis predicted a new cryptic splice site downstream of the original position generating a 10-base deletion from the beginning of exon 12; (c.1706-1715del.ATCTCCTCAG). cDNA sequencing of exon 12 confirmed the computational analysis. The deletion was visualized on 4% agarose gel. The deletion generates a frameshift and a premature termination codon (c.1991-1993; p.(Asp569Valfs*93). RT-PCR revealed that LDLR mRNA is 9.3%±6.5 and 17.9%±8.0 for FH homozygote and heterozygote individuals respectively, compared to a healthy family control. We predict a class II LDLR mutation that leads to a truncated receptor missing exons 14-18. We called this mutation "the Arabic allele". We expect a significant contribution of this mutation to the prevalence of FH among Arabs. Also, we propose that the severe down regulation of LDLR mRNA expression is due to nonsense-mediated-decay.

THE ROLE OF PLASMA LEVELS INTERLEUKIN-6 ON MORTALITY IN NON-OBESE PATIENTS WITH NEWLY DIAGNOSED HEART FAILURE, DURING 12-MONTHS OF FOLLOW-UP

The most frequent form of monogenic hypercholesterolemia, also known as Familial Hypercholesterolemia (FH), is characterized by plasma accumulation of cholesterol transported in Low Density Lipoproteins (LDLs). FH has a co-dominant transmission with a gene-dosage effect. FH heterozygotes have levels of plasma LDL-cholesterol (LDL-C) twice normal and present xanthomas and coronary heart disease (CHD) in adulthood. In rare FH homozygotes plasma LDL-C level is four times normal, while xanthomas and CHD are present from infancy. Most FH patients are carriers of mutations of the LDL receptor (LDLR); a minority of them carry either mutations in the Apolipoprotein B (ApoB), the protein constituent of LDLs which is the ligand for LDLR, or gain of function mutations of PCSK9, the protein responsible for the intracellular degradation of the LDLR. From 1970 to the mid 90s some publications described children with the clinical features of homozygous FH, who were born from normocholesterolemic parents, strongly suggesting a recessive transmission of FH. In these patients the involvement of LDLR and APOB genes was excluded. Interestingly, several patients were identified in the island of Sardinia (Italy), whose population has a peculiar genetic background due to geographical isolation. In this review, starting from the early descriptions of patients with putative recessive hypercholesterolemia, we highlight the milestones that led to the identification of a novel gene involved in LDL metabolism and the characterization of its encoded protein. The latter turned out to be an adaptor protein required for the LDLR-mediated endocytosis of LDLs in hepatocytes. The loss of function of this protein is the cause of Autosomal Recessive Hypercholesterolemia (ARH).

Clinical course of homozygous familial hypercholesterolemia during childhood: report on 4 unrelated patients with homozygous or compound heterozygous mutations in theLDLR gene

Natural history of the disease in 4 unrelated Polish children with homozygous familial hypercholesterolemia (FH) is described. Their phenotypic homozygosity was established by identification of known LDLR gene mutations on both alleles, respectively: p.G592E & p.G592E in Patient 1; p.G592E & p.C667Y in Patient 2; p.S177L & p.R350X in Patient 3; and p.G592E & deletion in the promoter region, exons 1 and 2 in Patient 4. Heterozygosity of the mutations was revealed in all patients' mothers and fathers (obligatory heterozygotes) and in 1 out of 4 siblings studied. FH was diagnosed at the age of 4 months to 9 years by cholesterol screening among family members of patients with early cardiovascular disease episodes. At the time of FH detection, the children were asymptomatic. Only in 2, some skin eruptions were found. Antihyperlipidemic therapy was started, including a lipid-lowering diet, cholestyramine, and HMG-CoA inhibitors if necessary. No cardiovascular symptoms appeared during the observation up to the age of 18, 20, 19, and 17 years, respectively. An increase in external carotid artery diameter was found in a patient at the age of 9 years, and LDL-apheresis was introduced in his therapy. We conclude that the analysis of LDLR gene mutations in the studied FH children made it possible to identify 4 presymptomatic FH homozygotes and to introduce early appropriate treatment. Multicenter analysis of such persons would finally determine if the early lipid-lowering procedures can significantly reduce the risk of premature cardiovascular disease in homozygous FH.

Two novel mutations 685del 1 and D129G in the low-density lipoprotein receptor gene in a compound heterozygote Chinese family with familial hypercholesterolemia

DNA sequencing analysis was used to scan the genes in a Chinese family with clinically diagnosed autosomal genetic hypercholesterolemia. Two mutations were identified in exon 4 of the low-density lipoprotein receptor gene, which is the possible molecular mechanism of etiology of the family. The proband's extremely high level of serum cholesterol and the related manifestations suggested that he was a familial hypercholesterolemia homozygote and that his parents were in a relatively milder condition. DNA sequencing revealed that the proband had an abnormal pattern of exon 4 of the low-density lipoprotein receptor gene due to a heterozygosity (A/G) at nucleotide 386 and a heterozygous single-base deletion (A) at 685. Nucleotide 386 is the second base of codon 129, and A-->G mutation (D129G) changed this codon from Asp(GAC) to Gly(GGC). The single-base deletion of A at 685 (685del 1) is a frameshift mutation. It changes the phase of triplets, so that all codons are misread after this site of mutation; consequently, the protein expressed by the gene must be abnormal in structure and function. DNA analysis of the other family members showed that the 2 mutations should be respectively located in different alleles of the proband. Both of the 2 mutations have not been reported previously.

Elevated serum levels of proinflammatory cytokines and biomarkers of matrix remodeling in never-treated patients with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a common inherited disorder of lipoprotein metabolism, whose origin involves mutations in the gene coding for the low-density lipoprotein receptor protein. Although FH is monogenic, wide variation occurs in the onset and severity of atherosclerosis in these patients. Since data on levels of inflammatory proteins and/or active factors in FH patients who have never received lipid-lowering treatment are lacking, serum levels of MMP-3, active MMP-9 and TIMP-1 as well as pro-inflammatory cytokines (TNF-alpha, IL-18) were determined in never-treated homozygous FH Moroccan patients (n=4) and compared to those of heterozygous FH subjects (n=7) and of healthy control subjects (n=5). When compared to controls, homozygous FH patients exhibited levels of active MMP-9 and TIMP-1 (p<0.05), and of both high sensitive-CRP and IL-18 which were significantly elevated (p<0.05 and p<0.01, respectively). In heterozygous FH patients, intermediate values between FH homozygotes and healthy controls were observed for these markers, with the exception of MMP-9 activity whose levels were significantly elevated (p<0.05). Multivariate analysis revealed a positive correlation between apolipoprotein B, TIMP-1 and IL-18 levels, and between hs-CRP and IL-18 (p<0.01). Although the sample size of this FH group was limited, our data suggest that nontreated homozygous FH patients, and to a lesser degree heterozygous FH patients, exhibit not only a markedly proinflammatory vascular state but also pronounced extracellular matrix remodeling, as reflected by elevated circulating levels of inflammatory cytokines and MMPs.

Mutations in low-density lipoprotein receptor gene as a cause of hypercholesterolemia in Taiwan

Familial hypercholesterolemia (FH) is inherited as an autosomal dominant trait that has been associated with more than 920 different mutations in the low-density lipoprotein receptor (LDLR) gene. To characterize LDLR gene mutations in the Chinese of Han descent with FH, we isolated genomic DNA from peripheral blood samples of 20 affected subjects and 50 healthy subjects with no family history of hypercholesterolemia. We used polymerase chain reaction and long polymerase chain reaction to amplify the 18 coding exons and the minimal promoter of the LDLR gene, and subjected amplicons to direct sequence analysis. We identified 6 mutations in LDLR gene, including heterozygous missense mutations I420T (ATC-->ACC), C660W (TGC-->TGG), H562Y (CAC-->TAC), and A606T (GCC-->ACC), and a heterozygous and a homozygous mutation in codon P664L (CCG-->CTG) as well as a homozygous large deletion of exons 6 to 8. The FH homozygotes manifested generalized xanthomatosis. One of the mutations we identified (C660W) was novel. In conclusion, we identified 5 missense mutations and 1 large deletion in LDLR gene, including 1 novel mutation in Han Chinese with FH in Taiwan.

Increased production of VLDL apoB-100 in subjects with familial hypercholesterolemia carrying the same null LDL receptor gene mutation

Early radiokinetic studies revealed that the classical metabolic defect in patients with familial hypercholesterolemia (FH) is hypocatabolism of LDL due to decreased LDL receptor activity. However, recent studies have suggested that hepatic oversecretion of apolipoprotein B-100 (apoB-100)-containing lipoproteins could also contribute to the markedly elevated plasma concentrations of LDL-cholesterol found in FH. The aim of this study was to examine the kinetics of apoB-100 labeled with a stable isotope (l-[5,5,5-D(3)] leucine) in five normolipidemic controls and in seven well-characterized FH subjects that included six FH heterozygotes and one FH homozygote carrying the same null LDL receptor gene mutation. As compared with controls, the VLDL apoB-100 production rate was increased by 50% in the FH heterozygotes and by 109% in the FH homozygote. Furthermore, FH subjects had significantly higher LDL apoB-100 pool size and lower LDL apoB-100 fractional catabolic rate than controls. These results indicate that the elevation of plasma LDL-cholesterol found in FH is attributable to both decreased clearance of LDL and increased hepatic production of apoB-100-containing lipoproteins.