Update and Analysis of the University College London Low Density Lipoprotein Receptor Familial Hypercholesterolemia Database

Systematic cell-based phenotyping of missense alleles empowers rare variant association studies: a case for LDLR and myocardial infarction

A fundamental challenge to contemporary genetics is to distinguish rare missense alleles that disrupt protein functions from the majority of alleles neutral on protein activities. High-throughput experimental tools to securely discriminate between disruptive and non-disruptive missense alleles are currently missing. Here we establish a scalable cell-based strategy to profile the biological effects and likely disease relevance of rare missense variants in vitro. We apply this strategy to systematically characterize missense alleles in the low-density lipoprotein receptor (LDLR) gene identified through exome sequencing of 3,235 individuals and exome-chip profiling of 39,186 individuals. Our strategy reliably identifies disruptive missense alleles, and disruptive-allele carriers have higher plasma LDL-cholesterol (LDL-C). Importantly, considering experimental data refined the risk of rare LDLR allele carriers from 4.5- to 25.3-fold for high LDL-C, and from 2.1- to 20-fold for early-onset myocardial infarction. Our study generates proof-of-concept that systematic functional variant profiling may empower rare variant-association studies by orders of magnitude.

Exome sequencing has proven powerful to identify protein-coding variation across the human genome, unravel the basis of monogenic diseases and discover rare alleles that confer risk for complex disease. Nevertheless, two key challenges limit its application to complex phenotypes: first, most alleles identified in a population are extremely rare; and second, most alleles are neutral on protein activities. Consequently, association tests that rely on enumerating rare alleles in cases and controls (termed rare variant association studies, RVAS) are typically underpowered, as the many neutral alleles dampen signals that arise from the few alleles that disrupt protein functions. Strategies to securely discriminate disruptive from neutral variants are immature, in particular for missense variants. Here we show that the statistical power of RVAS improves dramatically if variants are stratified according to their in vitro ascertained functions. We establish scalable technology to objectively profile the biological effects of exome-identified missense variants in the low-density lipoprotein receptor (LDLR) through systematic overexpression and complementation experiments in cells. We demonstrate that carriers of LDLR alleles, which our experiments identify as “disruptive-missense”, have higher plasma LDL-C, and that considering in vitro data may make it possible to reduce RVAS sample sizes by more than 2-fold.

Tumor necrosis factor beta NcoI polymorphism (rs909253) is associated with inflammatory and metabolic markers in acute ischemic stroke

Polymorphisms in genes coding for pro-inflammatory molecules represent important factors for the pathogenesis and outcome of stroke. The aim of this study was to evaluate the relationship between the tumor necrosis factor beta (TNF-β) NcoI (rs909253) polymorphism with inflammatory and metabolic markers in acute ischemic stroke. Ninety-three patients and 134 controls were included. The TNF-β polymorphism was determined using PCR-RFLP with NcoI restriction enzyme. Stroke subtypes and neurological deficit score were evaluated. White blood cell counts, erythrocyte sedimentation rate (ESR), plasma levels of IL-6 and TNF-α, serum high sensitivity C-reactive Protein (hsCRP), serum lipid profile, plasma levels of glucose and insulin, and homeostatic model assessment of insulin resistance (HOMA-IR) were determined. Stroke patients presented higher white blood cell counts, hsCRP, ESR, glucose, insulin, and HOMA-IR, and lower HDL cholesterol than controls (p < 0.01). There was no difference in genotypic and allelic frequency of TNF-β NcoI polymorphism among patients and controls (p > 0.05). However, stroke patients carrying the TNFB2/B2 genotype presented higher levels of TNF-α, white blood cell counts, total cholesterol, LDL cholesterol, glucose, insulin, and HOMA-IR than those with other genotypes (p < 0.05). White blood cells, IL-6, hsCRP, and ESR were positively correlated with the neurological deficit of the patients (p < 0.05). Taken together, TNF-β NcoI polymorphism, by itself, was not associated with increased susceptibility for stroke development. However, the homozygous genotype for the allele TNFB2 was associated with higher expression of classical inflammatory and metabolic markers of development and outcome of stroke than other genotypes. The identification of variant alleles might allow both better prediction of susceptibility for stroke as well the identification of novel stroke mechanisms that could be target to new therapeutic approaches. Stroke patients carrying the TNFB2 variant allele could have a beneficial effect with the anti-inflammatory therapies in the early inflammatory phase of stroke.

Exome sequencing in suspected monogenic dyslipidemias

BACKGROUND

Exome sequencing is a promising tool for gene mapping in Mendelian disorders. We used this technique in an attempt to identify novel genes underlying monogenic dyslipidemias.

METHODS AND RESULTS

We performed exome sequencing on 213 selected family members from 41 kindreds with suspected Mendelian inheritance of extreme levels of low-density lipoprotein cholesterol (after candidate gene sequencing excluded known genetic causes for high low-density lipoprotein cholesterol families) or high-density lipoprotein cholesterol. We used standard analytic approaches to identify candidate variants and also assigned a polygenic score to each individual to account for their burden of common genetic variants known to influence lipid levels. In 9 families, we identified likely pathogenic variants in known lipid genes (ABCA1, APOB, APOE, LDLR, LIPA, and PCSK9); however, we were unable to identify obvious genetic etiologies in the remaining 32 families, despite follow-up analyses. We identified 3 factors that limited novel gene discovery: (1) imperfect sequencing coverage across the exome hid potentially causal variants; (2) large numbers of shared rare alleles within families obfuscated causal variant identification; and (3) individuals from 15% of families carried a significant burden of common lipid-related alleles, suggesting complex inheritance can masquerade as monogenic disease.

CONCLUSIONS

We identified the genetic basis of disease in 9 of 41 families; however, none of these represented novel gene discoveries. Our results highlight the promise and limitations of exome sequencing as a discovery technique in suspected monogenic dyslipidemias. Considering the confounders identified may inform the design of future exome sequencing studies.

PCSK9 inhibition with evolocumab (AMG 145) in heterozygous familial hypercholesterolaemia (RUTHERFORD-2): a randomised, double-blind, placebo-controlled trial

BACKGROUND

Heterozygous familial hypercholesterolaemia is characterised by low cellular uptake of LDL cholesterol, increased plasma LDL cholesterol concentrations, and premature cardiovascular disease. Despite intensive statin therapy, with or without ezetimibe, many patients are unable to achieve recommended target levels of LDL cholesterol. We investigated the effect of PCSK9 inhibition with evolocumab (AMG 145) on LDL cholesterol in patients with this disorder.

METHODS

This multicentre, randomised, double-blind, placebo-controlled trial was undertaken at 39 sites (most of which were specialised lipid clinics, mainly attached to academic institutions) in Australia, Asia, Europe, New Zealand, North America, and South Africa between Feb 7 and Dec 19, 2013. 331 eligible patients (18-80 years of age), who met clinical criteria for heterozygous familial hypercholesterolaemia and were on stable lipid-lowering therapy for at least 4 weeks, with a fasting LDL cholesterol concentration of 2·6 mmol/L or higher, were randomly allocated in a 2:2:1:1 ratio to receive subcutaneous evolocumab 140 mg every 2 weeks, evolocumab 420 mg monthly, or subcutaneous placebo every 2 weeks or monthly for 12 weeks. Randomisation was computer generated by the study sponsor, implemented by a computerised voice interactive system, and stratified by LDL cholesterol concentration at screening (higher or lower than 4·1 mmol/L) and by baseline ezetimibe use (yes/no). Patients, study personnel, investigators, and Amgen study staff were masked to treatment assignments within dosing frequency groups. The coprimary endpoints were percentage change from baseline in LDL cholesterol at week 12 and at the mean of weeks 10 and 12, analysed by intention-to-treat. This trial is registered with ClinicalTrials.gov, number NCT01763918.

FINDINGS

Of 415 screened patients, 331 were eligible and were randomly assigned to the four treatment groups: evolocumab 140 mg every 2 weeks (n=111), evolocumab 420 mg monthly (n=110), placebo every 2 weeks (n=55), or placebo monthly (n=55). 329 patients received at least one dose of study drug. Compared with placebo, evolocumab at both dosing schedules led to a significant reduction in mean LDL cholesterol at week 12 (every-2-weeks dose: 59·2% reduction [95% CI 53·4-65·1], monthly dose: 61·3% reduction [53·6-69·0]; both p<0·0001) and at the mean of weeks 10 and 12 (60·2% reduction [95% CI 54·5-65·8] and 65·6% reduction [59·8-71·3]; both p<0·0001). Evolocumab was well tolerated, with rates of adverse events similar to placebo. The most common adverse events occurring more frequently in the evolocumab-treated patients than in the placebo groups were nasopharyngitis (in 19 patients [9%] vs five [5%] in the placebo group) and muscle-related adverse events (ten patients [5%] vs 1 [1%]).

INTERPRETATION

In patients with heterozygous familial hypercholesterolaemia, evolocumab administered either 140 mg every 2 weeks or 420 mg monthly was well tolerated and yielded similar and rapid 60% reductions in LDL cholesterol compared with placebo.

FUNDING

Amgen Inc.

Activity-associated effect of LDL receptor missense variants located in the cysteine-rich repeats

BACKGROUND

The LDL receptor (LDLR) is a Class I transmembrane protein critical for the clearance of cholesterol-containing lipoprotein particles. The N-terminal domain of the LDLR harbours the ligand-binding domain consisting of seven cysteine-rich repeats of approximately 40 amino acids each. Mutations in the LDLR binding domain may result in loss of receptor activity leading to familial hypercholesterolemia (FH). In this study the activity of six mutations located in the cysteine-rich repeats of the LDLR has been investigated.

METHODS

CHO-ldlA7 transfected cells with six different LDLR mutations have been used to analyse in vitro LDLR expression, lipoprotein binding and uptake. Immunoblotting of cell extracts, flow cytometry and confocal microscopy have been performed to determine the effects of these mutations. In silico analysis was also performed to predict the mutation effect.

RESULTS AND CONCLUSION

From the six mutations, p.Arg257Trp turned out to be a non-pathogenic LDLR variant whereas p.Cys116Arg, p.Asp168Asn, p.Asp172Asn, p.Arg300Gly and p.Asp301Gly were classified as binding-defective LDLR variants whose effect is not as severe as null allele mutations.

Exome sequencing identifies rare LDLR and APOA5 alleles conferring risk for myocardial infarction

Myocardial infarction (MI), a leading cause of death around the world, displays a complex pattern of inheritance. When MI occurs early in life, genetic inheritance is a major component to risk. Previously, rare mutations in low-density lipoprotein (LDL) genes have been shown to contribute to MI risk in individual families, whereas common variants at more than 45 loci have been associated with MI risk in the population. Here we evaluate how rare mutations contribute to early-onset MI risk in the population. We sequenced the protein-coding regions of 9,793 genomes from patients with MI at an early age (≤50 years in males and ≤60 years in females) along with MI-free controls. We identified two genes in which rare coding-sequence mutations were more frequent in MI cases versus controls at exome-wide significance. At low-density lipoprotein receptor (LDLR), carriers of rare non-synonymous mutations were at 4.2-fold increased risk for MI; carriers of null alleles at LDLR were at even higher risk (13-fold difference). Approximately 2% of early MI cases harbour a rare, damaging mutation in LDLR; this estimate is similar to one made more than 40 years ago using an analysis of total cholesterol. Among controls, about 1 in 217 carried an LDLR coding-sequence mutation and had plasma LDL cholesterol > 190 mg dl(-1). At apolipoprotein A-V (APOA5), carriers of rare non-synonymous mutations were at 2.2-fold increased risk for MI. When compared with non-carriers, LDLR mutation carriers had higher plasma LDL cholesterol, whereas APOA5 mutation carriers had higher plasma triglycerides. Recent evidence has connected MI risk with coding-sequence mutations at two genes functionally related to APOA5, namely lipoprotein lipase and apolipoprotein C-III (refs 18, 19). Combined, these observations suggest that, as well as LDL cholesterol, disordered metabolism of triglyceride-rich lipoproteins contributes to MI risk.

A Mechanistic Systems Pharmacology Model for Prediction of LDL Cholesterol Lowering by PCSK9 Antagonism in Human Dyslipidemic Populations

PCSK9 is a promising target for the treatment of hyperlipidemia and cardiovascular disease. A Quantitative Systems Pharmacology model of the mechanisms of action of statin and anti-PCSK9 therapies was developed to predict low density lipoprotein (LDL) changes in response to anti-PCSK9 mAb for different treatment protocols and patient subpopulations. Mechanistic interactions and cross-regulation of LDL, LDL receptor, and PCSK9 were modeled, and numerous virtual subjects were developed and validated against clinical data. Simulations predict a slightly greater maximum percent reduction in LDL cholesterol (LDLc) when anti-PCSK9 is administered on statin background therapy compared to as a monotherapy. The difference results primarily from higher PCSK9 levels in patients on statin background. However, higher PCSK9 levels are also predicted to increase clearance of anti-PCSK9, resulting in a faster rebound of LDLc. Simulations of subjects with impaired LDL receptor (LDLR) function predict compromised anti-PCSK9 responses in patients such as homozygous familial hypercholesterolemics, whose functional LDLR is below 10% of normal.

Identification of a novel nonsense variant c.1332dup, p.(D445*) in the LDLR gene that causes familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal dominant disease predominantly caused by a mutation in the low-density lipoprotein receptor (LDLR) gene. Here, we describe two severely affected FH patients who were resistant to statin therapy and were managed on an apheresis program. We identified a novel duplication variant c.1332dup, p.(D445*) at exon 9 and a known silent variant c.1413A>G, p.(=), rs5930, NM_001195798.1 at exon 10 of the LDLR gene in both patients.

Advantages and versatility of fluorescence-based methodology to characterize the functionality of LDLR and class mutation assignment

Familial hypercholesterolemia (FH) is a common autosomal codominant disease with a frequency of 1:500 individuals in its heterozygous form. The genetic basis of FH is most commonly mutations within the LDLR gene. Assessing the pathogenicity of LDLR variants is particularly important to give a patient a definitive diagnosis of FH. Current studies of LDLR activity ex vivo are based on the analysis of 125I-labeled lipoproteins (reference method) or fluorescent-labelled LDL. The main purpose of this study was to compare the effectiveness of these two methods to assess LDLR functionality in order to validate a functional assay to analyse LDLR mutations. LDLR activity of different variants has been studied by flow cytometry using FITC-labelled LDL and compared with studies performed previously with 125I-labeled lipoproteins. Flow cytometry results are in full agreement with the data obtained by the 125I methodology. Additionally confocal microscopy allowed the assignment of different class mutation to the variants assayed. Use of fluorescence yielded similar results than 125I-labeled lipoproteins concerning LDLR activity determination, and also allows class mutation classification. The use of FITC-labelled LDL is easier in handling and disposal, cheaper than radioactivity and can be routinely performed by any group doing LDLR functional validations.

An update on the clinical development of proprotein convertase subtilisin kexin 9 inhibitors, novel therapeutic agents for lowering low-density lipoprotein cholesterol

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an essential role in the degradation of low-density lipoprotein C (LDL-C) receptors, and PCSK9 inhibitors have recently emerged as a potential treatment option to reduce LDL-C. Our paper reviewed the current available Phase II clinical trials of PCSK9 inhibitors for the treatment of dyslipidemia. A second objective of this review was to evaluate the potential clinical role of PCSK9 inhibitors in the management of dyslipidemia. Studies evaluating the efficacy and safety of any PCSK9 inhibitors in patients with dyslipidemia were included. The monoclonal antibodies REGN727/SAR236553 and AMG145 have the most published clinical data. Seven phase II trials were retrieved that evaluated the efficacy and safety of REGN727/SAR236553 or AMG145 in patients with either hypercholesterolemia or heterozygous familial hypercholesterolemia (HeFH). These two agents significantly decreased LDL-C levels either as monotherapy or in combination with other lipid-lowering agents. REGN727/SAR236553 and AMG145 have been well tolerated. The ongoing phase III trials of these two agents are summarized. REGN727/SAR236553 and AMG145 have demonstrated the potential to further decrease LDL-C levels when added to conventional lipid-lowering therapy. Morbidity and mortality data are required to define their roles in clinical practice.

Functional analysis of four LDLR 5'UTR and promoter variants in patients with familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is an autosomal dominant inherited disease characterised by increased low-density lipoprotein cholesterol (LDL-C) levels. The functionality of four novel variants within the LDLR 5'UTR and promoter located at c.-13A>G, c.-101T>C, c.-121T>C and c.-215A>G was investigated using in silico and in vitro assays, and a systemic bioinformatics analysis of all 36 reported promoter variants are presented. Bioinformatic tools predicted that all four variants occurred in sites likely to bind transcription factors and that binding was altered by the variant allele. Luciferase assay was performed for all the variants. Compared with wild type, the c.-101T>C and c.-121T>C variants showed significantly lower mean (±SD) luciferase activity (64 ± 8 and 72 ± 8%, all P<0.001), suggesting that these variants are causal of the FH phenotype. No significant effect on gene expression was seen for the c.-13A>G or c.-215A>G variants (96 ± 15 and 100 ± 12%), suggesting these variants are not FH causing. Similar results were seen for the c.-101T>C and c.-121T>C variants in lipid-depleted serum. However, a significant reduction in luciferase activity was seen in the c.-215A>G variant in lipid-depleted serum. Electrophoretic-mobility shift assays identified allele-specific binding of liver (hepatoma) nuclear proteins to c.-121T>C and suggestive differential binding to c.-101T>C but no binding to c.-215A>G. These data highlight the importance of in vitro testing of reported LDLR promoter variants to establish their role in FH. The functional assays performed suggest that the c.-101T>C and c.-121T>C variants are pathogenic, whereas c.-13A>G variant is benign, and the status of c.-215A>G remains unclear.

Editing livestock genomes with site-specific nucleases

Over the past 5 years there has been a major transformation in our ability to precisely manipulate the genomes of animals. Efficiencies of introducing precise genetic alterations in large animal genomes have improved 100000-fold due to a succession of site-specific nucleases that introduce double-strand DNA breaks with a specificity of 10(-9). Herein we describe our applications of site-specific nucleases, especially transcription activator-like effector nucleases, to engineer specific alterations in the genomes of pigs and cows. We can introduce variable changes mediated by non-homologous end joining of DNA breaks to inactive genes. Alternatively, using homology-directed repair, we have introduced specific changes that support either precise alterations in a gene's encoded polypeptide, elimination of the gene or replacement by another unrelated DNA sequence. Depending on the gene and the mutation, we can achieve 10%-50% effective rates of precise mutations. Applications of the new precision genetics are extensive. Livestock now can be engineered with selected phenotypes that will augment their value and adaption to variable ecosystems. In addition, animals can be engineered to specifically mimic human diseases and disorders, which will accelerate the production of reliable drugs and devices. Moreover, animals can be engineered to become better providers of biomaterials used in the medical treatment of diseases and disorders.

Novel low density lipoprotein receptor variant linked to early onset acute myocardial infarction in a patient with familial hypercholesterolaemia

A novel LDL-receptor gene variant was found responsible for previously undetected familial hypercholesterolaemia and acute myocardial infarction in a young man.

Familial hypercholesterolemia: A review

Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism resulting in elevated serum low-density lipoprotein (LDL) cholesterol levels leading to increased risk for premature cardiovascular diseases (CVDs). The diagnosis of this condition is based on clinical features, family history, and elevated LDL-cholesterol levels aided more recently by genetic testing. As the atherosclerotic burden is dependent on the degree and duration of exposure to raised LDL-cholesterol levels, early diagnosis and initiation of treatment is paramount. Statins are presently the mainstay in the management of these patients, although newer drugs, LDL apheresis, and other investigational therapies may play a role in certain subsets of FH, which are challenging to treat. Together these novel treatments have notably improved the prognosis of FH, especially that of the heterozygous patients. Despite these achievements, a majority of children fail to attain targeted lipid goals owing to persistent shortcomings in diagnosis, monitoring, and treatment. This review aims to highlight the screening, diagnosis, goals of therapy, and management options in patients with FH.

Reciprocal regulation of endocytosis and metabolism

The cellular uptake of many nutrients and micronutrients governs both their cellular availability and their systemic homeostasis. The cellular rate of nutrient or ion uptake (e.g., glucose, Fe(3+), K(+)) or efflux (e.g., Na(+)) is governed by a complement of membrane transporters and receptors that show dynamic localization at both the plasma membrane and defined intracellular membrane compartments. Regulation of the rate and mechanism of endocytosis controls the amounts of these proteins on the cell surface, which in many cases determines nutrient uptake or secretion. Moreover, the metabolic action of diverse hormones is initiated upon binding to surface receptors that then undergo regulated endocytosis and show distinct signaling patterns once internalized. Here, we examine how the endocytosis of nutrient transporters and carriers as well as signaling receptors governs cellular metabolism and thereby systemic (whole-body) metabolite homeostasis.

Targeted genetic testing for familial hypercholesterolaemia using next generation sequencing: a population-based study

Background

Familial hypercholesterolaemia (FH) is a common Mendelian condition which, untreated, results in premature coronary heart disease. An estimated 88% of FH cases are undiagnosed in the UK. We previously validated a method for FH mutation detection in a lipid clinic population using next generation sequencing (NGS), but this did not address the challenge of identifying index cases in primary care where most undiagnosed patients receive healthcare. Here, we evaluate the targeted use of NGS as a potential route to diagnosis of FH in a primary care population subset selected for hypercholesterolaemia.

Methods

We used microfluidics-based PCR amplification coupled with NGS and multiplex ligation-dependent probe amplification (MLPA) to detect mutations in LDLR, APOB and PCSK9 in three phenotypic groups within the Generation Scotland: Scottish Family Health Study including 193 individuals with high total cholesterol, 232 with moderately high total cholesterol despite cholesterol-lowering therapy, and 192 normocholesterolaemic controls.

Results

Pathogenic mutations were found in 2.1% of hypercholesterolaemic individuals, in 2.2% of subjects on cholesterol-lowering therapy and in 42% of their available first-degree relatives. In addition, variants of uncertain clinical significance (VUCS) were detected in 1.4% of the hypercholesterolaemic and cholesterol-lowering therapy groups. No pathogenic variants or VUCS were detected in controls.

Conclusions

We demonstrated that population-based genetic testing using these protocols is able to deliver definitive molecular diagnoses of FH in individuals with high cholesterol or on cholesterol-lowering therapy. The lower cost and labour associated with NGS-based testing may increase the attractiveness of a population-based approach to FH detection compared to genetic testing with conventional sequencing. This could provide one route to increasing the present low percentage of FH cases with a genetic diagnosis.

Approaches for classifying DNA variants found by Sanger sequencing in a medical genetics laboratory

Diagnostic applications of DNA sequencing technologies present a powerful tool for the clinical management of patients. Applications range from better diagnostic classification to identification of therapeutic options, prediction of drug response and toxicity, and carrier testing. Although the advent of massively parallel sequencing technologies has increased the complexity of clinical interpretation of sequence variants by an order of magnitude, the annotation and interpretation of the clinical effects of identified genomic variants remain a challenge regardless of the sequencing technologies used to identify them. Here, we survey methodologies which assist in the diagnostic classification of DNA variants and propose a practical decision analytic protocol to assist in the classification of sequencing variants in a clinical setting. The methods include database queries, software tools for protein consequence, evolutionary conservation and pathogenicity prediction, familial segregation, case-control studies, and literature review. These methods are deliberately pragmatic as diagnostic constraints of clinically useful turnaround times generally preclude obtaining evidence from in vivo or in vitro functional experiments for variant assessment. Clinical considerations require that variant classification is stringent and rigorous, as misinterpretation may lead to inappropriate clinical consequences; thus, multiple parameters and lines of evidence are considered to determine potential biological significance.

Functional characterization of two low-density lipoprotein receptor gene mutations in two Chinese patients with familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is an autosomal dominant disease that primarily results from mutations in the low-density lipoprotein receptor (LDLR) gene. We investigated two unrelated Chinese FH patients using gene screening and functional analysis to reveal the pathogenicity and the mechanism by which these mutations cause FH.

METHODS

First, the LDLR gene was sequenced in these patients. Then, mutant receptors were transfected into human embryo kidney 293 (HEK-293) cells, and a confocal laser-scanning microscope was used to observe the localization of mutant proteins. Further, the expression and the internalization activity were analyzed by flow cytometry. Finally, LDLR protein expression and stability was detected by western blot.

RESULTS

Two different LDLR class 2B mutations were detected in two patients. The C201F mutation is a known mutation. However, the G615V mutation is novel. Flow cytometry showed that the expression and internalization activity of the mutant LDLRs were reduced to 73.6% and 82.6% for G615V and 33.2% and 33.5% for C201F, respectively.

CONCLUSIONS

This study identified two LDLR mutations in Chinese patients with FH and analyzed the relationship between the genotype and phenotype of these patients. We found that these mutant LDLRs were defective in transport, which led to a reduction in cholesterol clearance. These results increase our understanding of the mutational spectrum of FH in the Chinese population.

Efficacy and safety profile of evolocumab (AMG145), an injectable inhibitor of the proprotein convertase subtilisin/kexin type 9: the available clinical evidence

INTRODUCTION

Despite the proven efficacy of statins, they are often reported to be inadequate to achieve low-density lipoprotein cholesterol (LDL-C) goals (especially in high-risk patients). Moreover, a large number of subjects cannot tolerate statins or full doses of these drugs. Thus, there is a need for additional effective LDL-C reducing agents.

AREAS COVERED

Evolocumab (AMG145) is a monoclonal antibody inhibiting the proprotein convertase subtilisin/kexin type 9 that binds to the liver LDL receptor and prevents it from normal recycling by targeting it for degradation. Phase I and II trials revealed that its subcutaneous injection, either alone or in combination with statins, is able to reduce LDL-C from 40 to 80%, apolipoprotein B100 from 30 to 59% and lipoprotein(a) from 18 to 36% in a dose-dependent manner. The incidence of side effects seems to be low and mainly limited to nasopharyngitis, injection site pain, arthralgia and back pain.

EXPERT OPINION

Evolocumab is an innovative powerful lipid-lowering drug, additive to statins and with an apparently large therapeutic range associated to a low rate of mild adverse events. If available data will be confirmed in long-term trials with strong outcomes, Evolocumab will provide an essential tool to treat high-risk patients who need to reach ambitious LDL-C target.

Presence and type of low density lipoprotein receptor (LDLR) mutation influences the lipid profile and response to lipid-lowering therapy in Brazilian patients with heterozygous familial hypercholesterolemia

OBJECTIVES

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused mainly by LDLR mutations. This study assessed the influence of the presence and type of LDLR mutation on lipid profile and the response to lipid-lowering therapy in Brazilian patients with heterozygous FH.

METHODS

For 14 ± 3 months, 156 patients with heterozygous FH receiving atorvastatin were followed. Coding sequences of the LDLR gene were bidirectionally sequenced, and the type of LDLR mutations were classified according to their probable functional class.

RESULTS

The frequencies of the types of LDLR mutations were: null-mutation (n = 40, 25.6%), defective-mutation (n = 59, 37.8%), and without an identified mutation (n = 57, 36.6%). Baseline total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were higher in patients carrying a null mutation (9.9 ± 1.9 mmol/L, 7.9 ± 1.7 mmol/L), compared to those with a defective (8.9 ± 2.2 mmol/L, 7.0 ± 2.0 mmol/L), or no mutation (7.9 ± 1.9 mmol/L, 5.8 ± 1.9 mmol/L) (p < 0.001). After treatment, the proportion of patients attaining an LDL-C<3.4 mmol/L was significantly different among groups: null (22.5%), defective (27.1%), and without mutations (47.4%) (p = 0.02). The presence of LDLR mutations was independently associated with higher odds of not achieving the LDL-C cut-off (OR 9.07, 95% CI 1.41-58.16, p = 0.02).

CONCLUSIONS

Our findings indicate that the presence and type of LDLR mutations influence lipid profile and response to lipid-lowering therapy in Brazilian patients with heterozygous FH. Thus, more intensive care with pharmacological therapeutics should be performed in patients who have a molecular analysis indicating the presence of a LDLR mutation.

The biology of PCSK9 from the endoplasmic reticulum to lysosomes: new and emerging therapeutics to control low-density lipoprotein cholesterol

Proprotein convertase subtilisin/kexin type 9 (PCSK9) directly binds to the epidermal growth factor-like repeat A domain of low-density lipoprotein receptor and induces its degradation, thereby controlling circulating low-density lipoprotein cholesterol (LDL-C) concentration. Heterozygous loss-of-function mutations in PCSK9 can decrease the incidence of coronary heart disease by up to 88%, owing to lifelong reduction of LDL-C. Moreover, two subjects with PCSK9 loss-of-function mutations on both alleles, resulting in a total absence of functional PCSK9, were found to have extremely low circulating LDL-C levels without other apparent abnormalities. Accordingly, PCSK9 could represent a safe and effective pharmacological target to increase clearance of LDL-C and to reduce the risk of coronary heart disease. Recent clinical trials using anti-PCSK9 monoclonal antibodies that block the PCSK9:low-density lipoprotein receptor interaction were shown to considerably reduce LDL-C levels by up to 65% when given alone and by up to 72% in patients already receiving statin therapy. In this review, we will discuss how major scientific breakthroughs in PCSK9 cell biology have led to the development of new and forthcoming LDL-C-lowering pharmacological agents.

Detection of variations and identifying genomic breakpoints for large deletions in the LDLR by Ion Torrent semiconductor sequencing

OBJECTIVES

The aims of this study were to 1) compare LDLR variant detection between Ion Torrent Personal Genome Machine (PGM) sequencing and conventional methods used for familial hypercholesterolaemia (FH) diagnosis i.e. exon-by-exon sequence analysis and multiplex ligation-dependent probe amplification (MLPA) and 2) identify genomic breakpoints for 12 cases of large deletions in LDLR previously identified by MLPA.

METHODS

Thirty FH patient samples were selected, 22 with mutations previously determined. Primers were designed and optimised to generate six amplicons covering the entire LDLR and sequenced on a PGM. An additional twelve samples carrying MLPA variants were sequenced on the PGM followed by Sanger sequencing to establish the breakpoints.

RESULTS

A total of 2179 LDLR variants were identified in the 30 samples, with 383 variants in the region sequenced that was common to both PGM and Sanger methods. Three discrepancies were identified; two of these were identified by visual inspection of the BAM files, whilst the remaining discrepancy was likely an artefact of the PCR approach. Approximate genomic breakpoints for the 12 MLPA variants were identified using PGM sequencing, and Sanger sequencing of these regions established causative breakpoints. Eleven different rearrangements/mutational events were found, with eight out of eleven occurring in Alus. Two of the three samples with exons 2-6del had identical breakpoints. Two samples with exons 11-12del had unique breakpoints, indicating separate ancestral origin or mutational events.

CONCLUSIONS

This study showed that Ion Torrent PGM sequencing is an accurate and efficient method to detect LDLR variants while providing additional information such as genomic breakpoints.

Quality assessment of the genetic test for familial hypercholesterolemia in the Netherlands

Introduction. Familial hypercholesterolemia (FH) is an inherited disorder associated with a severely increased risk of cardiovascular disease. Although DNA test results in FH are associated with important medical and ethical consequences, data on accuracy of genetic tests is scarce. Methods. Therefore, we performed a prospective study to assess the overall accuracy of the DNA test used in the genetic cascade screening program for FH in The Netherlands. Individuals aged 18 years and older tested for one of the 5 most prevalent FH mutations, were included consecutively. DNA samples were analyzed by the reference and a counter-expertise laboratory following a standardized procedure. Results. 1003 cases were included. In the end, 317 (32%) carried an FH mutation, whereas in 686 (69%) samples no mutation was found. The overall accuracy of the reference laboratory was 99.8%, with two false positive results identified by the counter-expertise laboratory. Conclusion. The currently used mutation analysis is associated with a very low error rate. Therefore, we do not recommend routine use of duplicate testing.

Familial hypercholesterolemia affects microvascular autoregulation in children

OBJECTIVE

Familial hypercholesterolemia (FH) impairs macrovascular endothelial function in childhood and causes an increase of cardiovascular risk in later life. Whether microvascular function is affected in children with FH is unknown. The aim of this study was to investigate the impact of FH on microvascular autoregulation in children by post occlusive reactive hyperemia (PORH).

METHODS

PORH of the skin was assessed using laser Doppler fluxmetry. Baseline perfusion, biological zero, defined as no-flow laser Doppler signal during suprasystolic occlusion, peak perfusion after release of suprasystolic occlusion, as well as time to peak perfusion and recovery time, defined as time until baseline perfusion is resumed, were measured in 16 children, who were diagnosed with FH according to current guidelines, and in 91 healthy controls.

RESULTS

In children with FH, peak perfusion was higher (FH: 1.60±0.68 vs. controls: 1.26±0.50 AU [arbitrary units], p=0.02), recovery time was longer (110±42.61 vs. 83.18±35.08 s, p=0.01) and biological zero was lower than in controls (0.12±0.04 vs. 0.18±0.05 AU, p<0.001). Baseline perfusion and time to peak were not different between children with FH and controls (baseline perfusion: 0.43±0.21 vs. 0.38±0.15 AU, p=0.18; time to peak: 15.44±12.25 vs. 18.18±17.79 s, p=0.56).

CONCLUSION

For the first time the present study reveals an impact of FH on microvascular autoregulation in children: the differences of PORH between children with FH and controls indicate an affected autoregulation of microvascular blood flow in FH, which has its onset in childhood.

The use of next-generation sequencing in clinical diagnosis of familial hypercholesterolemia

Purpose:

Familial hypercholesterolemia is a common Mendelian disorder associated with early-onset coronary heart disease that can be treated by cholesterol-lowering drugs. The majority of cases in the United Kingdom are currently without a molecular diagnosis, which is partly due to the cost and time associated with standard screening techniques. The main purpose of this study was to test the sensitivity and specificity of two next-generation sequencing protocols for genetic diagnosis of familial hypercholesterolemia.

Methods:

Libraries were prepared for next-generation sequencing by two target enrichment protocols; one using the SureSelect Target Enrichment System and the other using the PCR-based Access Array platform.

Results:

In the validation cohort, both protocols showed 100% specificity, whereas the sensitivity for short variant detection was 100% for the SureSelect Target Enrichment and 98% for the Access Array protocol. Large deletions/duplications were only detected using the SureSelect Target Enrichment protocol. In the prospective cohort, the mutation detection rate using the Access Array was highest in patients with clinically definite familial hypercholesterolemia (67%), followed by patients with possible familial hypercholesterolemia (26%).

Conclusion:

We have shown the potential of target enrichment methods combined with next-generation sequencing for molecular diagnosis of familial hypercholesterolemia. Adopting these assays for patients with suspected familial hypercholesterolemia could improve cost-effectiveness and increase the overall number of patients with a molecular diagnosis.

Genet Med 15 12, 948–957.

Elevated PCSK9 levels in untreated patients with heterozygous or homozygous familial hypercholesterolemia and the response to high-dose statin therapy

BACKGROUND

Proprotein convertase subtilisin kexin type 9 (PCSK9) is an enzyme that impairs low-density lipoprotein cholesterol (LDL-C) clearance from the plasma by promoting LDL receptor degradation. Patients with familial hypercholesterolemia (FH) have reduced or absent LDL receptors and should therefore have elevated PCSK9 levels.

METHODS AND RESULTS

Fasting lipograms and PCSK9 levels were measured 51 homozygous FH (HoFH), 20 heterozygous FH (HeFH), and 20 normocholesterolemic control subjects. Levels were repeated following high-dose statin therapy. LDL-C levels were significantly higher in untreated HoFH (13.4±0.7 mmol/L) and HeFH patients (7.0±0.2 mmol/L) compared with controls (2.6±0.1 mmol/L) (P<0.01). Statin therapy decreased LDL-C levels from 13.4±0.7 to 11.1±0.7 mmol/L in HoFH and from 7.0±0.2 to 3.6±0.2 mmol/L in HeFH patients (P<0.01). PCSK9 levels were higher in untreated HoFH (279±27 ng/mL) and HeFH (202±14 ng/mL) than in controls (132±10 ng/mL) (both P<0.01). High-dose statin therapy increased PCSK9 levels from 279±27 to 338±50 ng/mL in HoFH, and significantly so in the HeFH patients from 202±14 to 278±20 ng/mL (P<0.01). Linear regression analysis showed a correlation between PCSK9 and LDL-C (r=0.6769; P<0.0001); however, this was eliminated following statin therapy (r=0.2972; P=0.0625).

CONCLUSIONS

PCSK9 levels are elevated in untreated FH patients, particularly in those with HoFH. High-dose statin therapy further increases PCSK9 levels. PCSK9 inhibitors might be a beneficial therapy for FH patients, even in those with HoFH.

Analysis of the frequency and spectrum of mutations recognised to cause familial hypercholesterolaemia in routine clinical practice in a UK specialist hospital lipid clinic

Aim

To determine the frequency and spectrum of mutations causing Familial Hypercholesterolaemia (FH) in patients attending a single UK specialist hospital lipid clinic in Oxford and to identify characteristics contributing to a high mutation detection rate.

Methods

289 patients (272 probands) were screened sequentially over a 2-year period for mutations in LDLR, APOB and PCSK9 using standard molecular genetic techniques. The Simon Broome (SB) clinical diagnostic criteria were used to classify patients and a separate cohort of 409 FH patients was used for replication.

Results

An FH-causing mutation was found in 101 unrelated patients (LDLR = 54 different mutations, APOB p.(Arg3527Gln) = 10, PCSK9 p.(Asp374Tyr) = 0). In the 60 SB Definite FH patients the mutation detection rate was 73% while in the 142 with Possible FH the rate was significantly lower (27%, p < 0.0001), but similar (14%, p = 0.06) to the 70 in whom there was insufficient data to make a clinical diagnosis. The mutation detection rate varied significantly (p = 9.83 × 10⁻⁵) by untreated total cholesterol (TC) levels (25% in those <8.1 mmol/l and 74% in those >10.0 mmol/l), and by triglyceride levels (20% in those >2.16 mmol/l and 60% in those <1.0 mmol/l (p = 0.0005)), with both effects confirmed in the replication sample (p for trend = 0.0001 and p = 1.8 × 10⁻⁶ respectively). There was no difference in the specificity or sensitivity of the SB criteria versus the Dutch Lipid Clinic Network score in identifying mutation carriers (A_ROC respectively 0.73 and 0.72, p = 0.68).

Conclusions

In this genetically heterogeneous cohort of FH patients the mutation detection rate was significantly dependent on pre-treatment TC and triglyceride levels.

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54 different LDLR mutations found in a cohort of 272 FH probands.

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The cohort was found to be genetically heterogeneous with no specific FH mutation.

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Mutation detection rate was highly dependent on pre-treatment TC and TG levels.

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No difference in specificity/sensitivity between 2 clinical FH diagnosis approaches.

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Inadequate LDL-C reduction marks the need for more effective lipid-lowering therapy.

Mitotic spindle defects and chromosome mis-segregation induced by LDL/cholesterol-implications for Niemann-Pick C1, Alzheimer's disease, and atherosclerosis

Elevated low-density lipoprotein (LDL)-cholesterol is a risk factor for both Alzheimer's disease (AD) and Atherosclerosis (CVD), suggesting a common lipid-sensitive step in their pathogenesis. Previous results show that AD and CVD also share a cell cycle defect: chromosome instability and up to 30% aneuploidy-in neurons and other cells in AD and in smooth muscle cells in atherosclerotic plaques in CVD. Indeed, specific degeneration of aneuploid neurons accounts for 90% of neuronal loss in AD brain, indicating that aneuploidy underlies AD neurodegeneration. Cell/mouse models of AD develop similar aneuploidy through amyloid-beta (Aß) inhibition of specific microtubule motors and consequent disruption of mitotic spindles. Here we tested the hypothesis that, like upregulated Aß, elevated LDL/cholesterol and altered intracellular cholesterol homeostasis also causes chromosomal instability. Specifically we found that: 1) high dietary cholesterol induces aneuploidy in mice, satisfying the hypothesis' first prediction, 2) Niemann-Pick C1 patients accumulate aneuploid fibroblasts, neurons, and glia, demonstrating a similar aneugenic effect of intracellular cholesterol accumulation in humans 3) oxidized LDL, LDL, and cholesterol, but not high-density lipoprotein (HDL), induce chromosome mis-segregation and aneuploidy in cultured cells, including neuronal precursors, indicating that LDL/cholesterol directly affects the cell cycle, 4) LDL-induced aneuploidy requires the LDL receptor, but not Aß, showing that LDL works differently than Aß, with the same end result, 5) cholesterol treatment disrupts the structure of the mitotic spindle, providing a cell biological mechanism for its aneugenic activity, and 6) ethanol or calcium chelation attenuates lipoprotein-induced chromosome mis-segregation, providing molecular insights into cholesterol's aneugenic mechanism, specifically through its rigidifying effect on the cell membrane, and potentially explaining why ethanol consumption reduces the risk of developing atherosclerosis or AD. These results suggest a novel, cell cycle mechanism by which aberrant cholesterol homeostasis promotes neurodegeneration and atherosclerosis by disrupting chromosome segregation and potentially other aspects of microtubule physiology.

Genetic polymorphisms in LDLR, APOB, PCSK9 and other lipid related genes associated with familial hypercholesterolemia in Malaysia

Familial hypercholesterolemia (FH) is an autosomal dominant disorder characterized by elevations in total cholesterol (TC) and low density lipoprotein cholesterol (LDLc). Development of FH can result in the increase of risk for premature cardiovascular diseases (CVD). FH is primarily caused by genetic variations in Low Density Lipoprotein Receptor (LDLR), Apolipoprotein B (APOB) or Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) genes. Although FH has been extensively studied in the Caucasian population, there are limited reports of FH mutations in the Asian population. We investigated the association of previously reported genetic variants that are involved in lipid regulation in our study cohort. A total of 1536 polymorphisms previously implicated in FH were evaluated in 141 consecutive patients with clinical FH (defined by the Dutch Lipid Clinic Network criteria) and 111 unrelated control subjects without FH using high throughput microarray genotyping platform. Fourteen Single Nucleotide Polymorphisms (SNPs) were found to be significantly associated with FH, eleven with increased FH risk and three with decreased FH risk. Of the eleven SNPs associated with an increased risk of FH, only one SNP was found in the LDLR gene, seven in the APOB gene and three in the PCSK9 gene. SNP rs12720762 in APOB gene is associated with the highest risk of FH (odds ratio 14.78, p<0.001). Amongst the FH cases, 108 out of 141 (76.60%) have had at least one significant risk-associated SNP. Our study adds new information and knowledge on the genetic polymorphisms amongst Asians with FH, which may serve as potential markers in risk prediction and disease management.

GIGI: an approach to effective imputation of dense genotypes on large pedigrees

Recent emergence of the common-disease-rare-variant hypothesis has renewed interest in the use of large pedigrees for identifying rare causal variants. Genotyping with modern sequencing platforms is increasingly common in the search for such variants but remains expensive and often is limited to only a few subjects per pedigree. In population-based samples, genotype imputation is widely used so that additional genotyping is not needed. We now introduce an analogous approach that enables computationally efficient imputation in large pedigrees. Our approach samples inheritance vectors (IVs) from a Markov Chain Monte Carlo sampler by conditioning on genotypes from a sparse set of framework markers. Missing genotypes are probabilistically inferred from these IVs along with observed dense genotypes that are available on a subset of subjects. We implemented our approach in the Genotype Imputation Given Inheritance (GIGI) program and evaluated the approach on both simulated and real large pedigrees. With a real pedigree, we also compared imputed results obtained from this approach with those from the population-based imputation program BEAGLE. We demonstrated that our pedigree-based approach imputes many alleles with high accuracy. It is much more accurate for calling rare alleles than is population-based imputation and does not require an outside reference sample. We also evaluated the effect of varying other parameters, including the marker type and density of the framework panel, threshold for calling genotypes, and population allele frequencies. By leveraging information from existing genotypes already assayed on large pedigrees, our approach can facilitate cost-effective use of sequence data in the pursuit of rare causal variants.

A DNA microarray for the detection of point mutations and copy number variation causing familial hypercholesterolemia in Europe

To facilitate genetic cascade screening for familial hypercholesterolemia (FH) in Europe, two versions (7 and 9) of a DNA microarray were developed to detect the most frequent point mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin 9 (PCSK9) genes. The design of these microarrays is based on LIPOchip, version 4, which detects 191 LDLR and APOB mutations identified in Spanish patients with FH. A major improvement of LIPOchip, versions 7 and 9, is the ability to detect copy number variation (deletions or duplications of entire exons) in LDLR, thus abolishing the need to perform multiplex ligase-dependent probe amplification in patients with FH. The aim of this study was to validate a tool capable of detecting point mutations and copy number variations simultaneously and to evaluate its use and the newly developed software for analysis in clinical practice by reanalysis of several patients with known mutations causing FH. With the help of these validations, several aspects were analyzed, improved, and implemented in a newer version, which was evaluated through an internal validation.

The genetic spectrum of familial hypercholesterolemia in Pakistan

Background

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the genes coding for the low density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type-9 (PCSK9) or apo-lipoprotein B-100 (APOB). The aim of the present work was to determine the genetic basis of dyslipidemia in 11 unrelated Pakistani families.

Methods

High resolution melting (HRM), sequencing and restriction fragment length polymorphism (RFLP).

Results

Probands were screened for the promoter and all coding regions, including intron/exon boundaries, of LDLR and PCSK9 and part of exon 26 of APOB including p.(R3527Q). Two families were identified with previously unreported LDLR mutations (c.1019_1020delinsTG, p.(C340L) and c.1634G>A, p.(G545E)). Both probands had tendon xanthomas or xanthelasma and/or a history of cardiovascular disease. Co-segregation with hypercholesterolemia was demonstrated in both families. In silico studies predicted these variations to be damaging. In two families, novel PCSK9 variations were identified (exon2; c.314G > A, p.(R105Q) and exon3; c.464C>T, p.(P155L)). In silico studies suggested both were likely to be damaging, and family members carrying the p.(105Q) allele had lower total cholesterol levels, suggesting this is a loss-of-function mutation. For c.464C>T p.(P155L) the small number of relatives available precluded any strong inference.

Conclusion

This report brings to seven the number of different LDLR mutations reported in FH patients from Pakistan and, as expected in this heterogeneous population, no common LDLR mutation has been identified.

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We examined the LDLR/PCSK9 genes in patients with FH from Pakistan.

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Two novel LDLR mutations both showed co-segregation with hypercholesterolemia.

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Two novel PCSK9 variations were found one of which was a loss of function mutation.

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This brings to 7 the number of molecular causes of FH in patients from Pakistan.

Pharmacogenetic aspects in familial hypercholesterolemia with the special focus on FHMarburg (FH p.W556R)

Objective

Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder caused by mutations in the low density lipoprotein receptor (LDLR) gene. FH is characterized by elevated plasma LDL cholesterol, premature atherosclerosis, and a high risk of premature myocardial infarction. In general, mutations within LDLR gene can cause five different classes of defects, namely: class I defect: no LDLR synthesis; class II defect: no LDLR transport; class III defect: no low density lipoprotein (LDL) to LDLR binding; class IV defect: no LDLR/LDL internalization; and class V defect: no LDLR recycling. One might expect that both the class of LDLR defect as well as the precise mutation influences the severity of hypercholesterolemia on one hand and the response on drug treatment on the other. To clarify this question we studied the effect of the LDLR mutation p.W556R in two heterozygote subjects.

Results

We found that two heterozygote FH patients with the LDLR mutation p.W556R causing a class II LDLR defect (transport defective LDLR) respond exceedingly well to the treatment with simvastatin 40 mg/ezetimibe 10 mg. There was a LDL cholesterol decrease of 55 and 64%, respectively. In contrast, two affected homozygote p.W556R FH patients, in the mean time undergoing LDL apheresis, had no response to statin but a 15% LDL cholesterol decrease on ezetimibe monotherapy.

Conclusions

The LDLR mutation p.W556R is a frequent and severe class II defect for FH. The affected homozygote FH patients have a total loss of the functional LDLR and—as expected—do not respond on statin therapy and require LDL apheresis. In contrast, heterozygote FH patients with the same LDLR defect respond exceedingly well to standard lipid-lowering therapy, illustrating that the knowledge of the primary LDLR defect enables us to foresee the expected drug effects.

Mipomersen and other therapies for the treatment of severe familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal dominant condition with a population prevalence of one in 300–500 (heterozygous) that is characterized by high levels of low-density lipoprotein (LDL) cholesterol, tendon xanthomata, and premature atherosclerosis and coronary heart disease (CHD). FH is caused mainly by mutations in the LDLR gene. However, mutations in other genes including APOB and PCSK9, can give rise to a similar phenotype. Homozygous FH with an estimated prevalence of one in a million is associated with severe hypercholesterolemia with accelerated atherosclerotic CHD in childhood and without treatment, death usually occurs before the age of 30 years. Current approaches for the treatment of homozygous FH include statin-based lipid-lowering therapies and LDL apheresis. Mipomersen is a second-generation antisense oligonucleotide (ASO) targeted to human apolipoprotein B (apoB)-100. This review provides an overview of the pathophysiology and current treatment options for familial hypercholesterolemia and describes novel therapeutic strategies focusing on mipomersen, an antisense apoB synthesis inhibitor. Mipomersen is distributed mainly to the liver where it silences apoB mRNA, thereby reducing hepatic apoB-100 and giving rise to reductions in plasma total cholesterol, LDL-cholesterol, and apoB concentrations in a dose-and time-dependent manner. Mipomersen has been shown to decrease apoB, LDL-cholesterol and lipoprotein(a) in patients with heterozygous and homozygous FH on maximally tolerated lipid-lowering therapy. The short-term efficacy and safety of mipomersen has been established, however, injection site reactions are common and concern exists regarding the long-term potential for hepatic steatosis with this ASO. In summary, mipomersen given alone or in combination with standard lipid-lowering medications shows promise as an adjunct therapy in patients with homozygous or refractory heterozygous FH at high risk of atherosclerotic CHD, who are not at target or are intolerant of statins.

Apolipoprotein B Synthesis Inhibition With Mipomersen in Heterozygous Familial Hypercholesterolemia

Background—

Heterozygous familial hypercholesterolemia (HeFH) is a common genetic disorder leading to premature coronary artery disease. Despite statins and additional lipid-lowering therapies, many HeFH patients fail to achieve low-density lipoprotein cholesterol (LDL-C) goals. We evaluated mipomersen, an apolipoprotein B synthesis inhibitor, to further lower LDL-C in HeFH patients with coronary artery disease.

Methods and Results—

This double-blind, placebo-controlled, phase 3 trial randomized patients with HeFH and coronary artery disease on maximally tolerated statin and LDL-C ≥2.6 mmol/L (≥100 mg/dL) to weekly subcutaneous mipomersen 200 mg or placebo (2:1) for 26 weeks. The primary end point was percent change in LDL-C from baseline at week 28. Safety assessments included adverse events, laboratory tests, and magnetic resonance imaging assessment of hepatic fat. Of 124 randomized patients (41 placebo, 83 mipomersen), 114 (41 placebo, 73 mipomersen) completed treatment. Mean (95% confidence interval) LDL-C decreased significantly with mipomersen (−28.0% [−34.0% to −22.1%] compared with 5.2% [−0.5% to 10.9%] increase with placebo; P <0.001). Mipomersen significantly reduced apolipoprotein B (−26.3%), total cholesterol (−19.4%), and lipoprotein(a) (−21.1%) compared with placebo (all P <0.001). No significant change occurred in high-density lipoprotein cholesterol. Adverse events included injection site reactions and influenza-like symptoms. Five mipomersen patients (6%) had 2 consecutive alanine aminotransferase values ≥3 times the upper limit of normal at least 7 days apart; none were associated with significant bilirubin increases. Hepatic fat content increased a median of 4.9% with mipomersen versus 0.4% with placebo ( P <0.001).

Conclusions—

Mipomersen is an effective therapy to further reduce apolipoprotein B–containing lipoproteins, including LDL and lipoprotein(a), in HeFH patients with coronary artery disease on statins and other lipid-lowering therapy. The significance of hepatic fat and transaminase increases remains uncertain at this time.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00706849.