Low-density Lipoprotein Receptor Variants Research Articles

Cellular and functional evaluation of LDLR missense variants reported in hypercholesterolemic patients demonstrates their hypomorphic impacts on trafficking and LDL internalization

BackgroundFamilial hypercholesterolemia (FH) is an autosomal dominant disorder characterized by increased LDL-cholesterol levels. About 85% of FH cases are caused by LDLR mutations encoding the low-density lipoprotein receptor (LDLR). LDLR is synthesized in the endoplasmic reticulum (ER) where it undergoes post-translational modifications and then transported through Golgi apparatus to the plasma membrane. Over 2900 LDLR variants have been reported in FH patients with limited information on the pathogenicity and functionality of many of them. This study aims to elucidate the cellular trafficking and functional implications of LDLR missense variants identified in suspected FH patients using biochemical and functional methods.MethodsWe used HeLa, HEK293T, and LDLR-deficient-CHO-ldlA7 cells to evaluate the subcellular localization and LDL internalization of ten LDLR missense variants (p.C167F, p.D178N, p.C243Y, p.E277K, p.G314R, p.H327Y, p.D477N, p.D622G, p.R744Q, and p.R814Q) reported in multiethnic suspected FH patients. We also analyzed the functional impact of three variants (p.D445E, p.D482H, and p.C677F), two of which previously shown to be retained in the ER.ResultsWe show that p.D622G, p.D482H, and p.C667F are largely retained in the ER whereas p.R744Q is partially retained. The other variants were predominantly localized to the plasma membrane. LDL internalization assays in CHO-ldlA7 cells indicate that p.D482H, p.C243Y, p.D622G, and p.C667F have quantitatively lost their ability to internalize Dil-LDL with the others (p.C167F, p.D178N, p.G314R, p.H327Y, p.D445E, p.D477N, p.R744Q and p.R814Q) showing significant losses except for p.E277K which retained full activity. However, the LDL internalization assay is only to able evaluate the impact of the variants on LDL internalization and not the exact functional defects such as failure to bind LDL. The data represented illustrate the hypomorphism nature of variants causing FH which may explain some of the variable expressivity of FH.ConclusionOur combinatorial approach of in silico, cellular, and functional analysis is a powerful strategy to determine pathogenicity and FH disease mechanisms which may provide opportunitites for novel therapeutic strategies.

Design and Pilot Results from Million Veteran Program Return Of Actionable Genetic Results (MVP-ROAR) Study

As a mega-biobank linked to a national healthcare system, the Million Veteran Program (MVP) can directly improve the health care of participants. To determine the feasibility and outcomes of returning medically actionable genetic results to MVP participants, the program launched the MVP Return Of Actionable Results (MVP-ROAR) Study, with familial hypercholesterolemia (FH) as an exemplar actionable condition. The MVP-ROAR Study consists of a completed single-arm pilot phase and an ongoing randomized clinical trial (RCT), in which MVP participants are recontacted and invited to receive clinical confirmatory gene sequencing testing and a telegenetic counseling intervention. The primary outcome of the RCT is 6-month change in low-density lipoprotein cholesterol (LDL-C) between participants receiving results at baseline and those receiving results after 6 months. The pilot developed processes to identify and recontact participants nationally with probable pathogenic variants in low-density lipoprotein receptor (LDLR) on the MVP genotype array, invite them to clinical confirmatory gene sequencing, and deliver a telegenetic counseling intervention. Among participants in the pilot phase, 8 (100%) had active statin prescriptions after 6 months. Results were shared with 16 first-degree family members. Six-month ΔLDL-C (low-density lipoprotein cholesterol) after the genetic counseling intervention was -37 mg/dL (95% CI: -12 to -61; p=0.03). The ongoing RCT will determine between-arm differences in this primary outcome. While underscoring the importance of clinical confirmation of research results, the pilot phase of the MVP-ROAR Study marks a turning point in MVP and demonstrates the feasibility of returning genetic results to participants and their providers. The ongoing RCT will contribute to understanding how such a program might improve patient health care and outcomes.

LDLR gene rearrangements in Czech FH patients likely arise from one mutational event

BackgroundLarge deletions and duplications within the low-density lipoprotein receptor (LDLR) gene make up approximately 10% of LDLR pathogenic variants found in Czech patients with familial hypercholesterolemia. The goal of this study was to test the hypothesis that all probands with each rearrangement share identical breakpoints inherited from a common ancestor and to determine the role of Alu repetitive elements in the generation of these rearrangements.MethodsThe breakpoint sequence was determined by PCR amplification and Sanger sequencing. To confirm the breakpoint position, an NGS analysis was performed. Haplotype analysis of common LDLR variants was performed using PCR and Sanger sequencing.ResultsThe breakpoints of 8 rearrangements within the LDLR gene were analysed, including the four most common LDLR rearrangements in the Czech population (number of probands ranging from 8 to 28), and four less common rearrangements (1–4 probands). Probands with a specific rearrangement shared identical breakpoint positions and haplotypes associated with the rearrangement, suggesting a shared origin from a common ancestor. All breakpoints except for one were located inside an Alu element. In 6 out of 8 breakpoints, there was high homology (≥ 70%) between the two Alu repeats in which the break occurred.ConclusionsThe most common rearrangements of the LDLR gene in the Czech population likely arose from one mutational event. Alu elements likely played a role in the generation of the majority of rearrangements inside the LDLR gene.

Novel LDLR variants affecting low density lipoprotein metabolism identified in familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is an autosomal dominant disease of lipid metabolism mainly caused by mutations in the low-density lipoprotein receptor (LDLR) gene. Genetic detection of patients with FH help with precise diagnosis and treatment, thus reducing the risk of coronary heart disease (CHD) and other related diseases. The study aimed to identify the causative gene mutations in a Chinese FH family and reveal the pathogenicity and the mechanism of these mutations. Whole exome sequencing was performed in a patient with severe lipid metabolism dysfunction seeking fertility guidance from a Chinese FH family. Two LDLR variants c.1875C > G (p.N625K; novel variant) and c.1448G > A (p.W483*) were identified in the family. Wildtype and mutant LDLR constructs were established by the site-direct mutagenesis technique. Functional studies were carried out by cell transfection to evaluate the impact of detected variants on LDLR activity. The two variants were proven to affect LDL uptake and binding, resulting in cholesterol clearance reduction to different degrees. According to The American College of Medical Genetics and Genomics (ACMG) Standards and Guidelines, the W483* variant was classified as "Pathogenic", while the N625K variant as "VUS". Our results provide novel experimental evidence of functional alteration by LDLR variants identified in our study and expand the mutational spectrum of LDLR mutation induced FH.

Screening and verifying the mutations in the LDLR and APOB genes in a Chinese family with familial hypercholesterolemia

BackgroundFamilial hypercholesterolemia (FH) is an autosomal dominant genetic disorder. The primary objective of this study was to identify the major pathogenic mutations in a Chinese family with FH.MethodsWhole-genome sequencing (WGS) was used to identify variants of FH-related genes, including low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin 9 (PCSK9). Bioinformatics software was used to predict signal peptides, transmembrane structures, and spatial construction information of the mutated sequences. Western blotting was performed on the mutant protein to determine the presence of the major structural domains of the LDLR. The PCSK9 and APOB genes were screened and analyzed. Moreover, the proband and his brother were treated with a PCSK9 inhibitor for 1 year, and the effect of the treatment on lipid levels was assessed.ResultsWGS revealed two potentially pathogenic mutations in the LDLR gene. One was a novel mutation, c.497delinsGGATCCCCCAGCTGCATCCCCCAG (p. Ala166fs), and the other was a known pathogenic mutation, c.2054C>T (p. Pro685Leu). Bioinformatics prediction and in vitro experiments revealed that the novel mutation could not be expressed on the cell membrane. Numerous gene variants were identified in the APOB gene that may have a significant impact on the family members with FH. Thus, it is suggested that the severe manifestation of FH in the proband primarily resulted from the cumulative genetic effects of variants in both LDLR and APOB. However, a subsequent study indicated that treatment with a PCSK9 inhibitor (Evolocumab) did not significantly reduce the blood lipid levels in the proband or his brother.ConclusionsThe cumulative effect of LDLR and APOB variants was the primary cause of elevated blood lipid levels in this family. However, PCSK9 inhibitor therapy did not appear to be beneficial for the proband. This study emphasizes the importance of genetic testing in determining the most suitable treatment options for patients with FH.

LDLR and PCSK9 3´UTR variants and their putative effects on microRNA molecular interactions in familial hypercholesterolemia: a computational approach.

Familial hypercholesterolemia (FH) is caused by pathogenic variants in low-density lipoprotein (LDL) receptor (LDLR) or its associated genes, including apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9), and LDLR adaptor protein 1 (LDLRAP1). However, approximately 40% of the FH patients clinically diagnosed (based on FH phenotypes) may not carry a causal variant in a FH-related gene. Variants located at 3' untranslated region (UTR) of FH-related genes could elucidate mechanisms involved in FH pathogenesis. This study used a computational approach to assess the effects of 3'UTR variants in FH-related genes on miRNAs molecular interactions and to explore the association of these variants with molecular diagnosis of FH. Exons and regulatory regions of FH-related genes were sequenced in 83 FH patients using an exon-target gene sequencing strategy. In silico prediction tools were used to study the effects of 3´UTR variants on interactions between miRNAs and target mRNAs. Pathogenic variants in FH-related genes (molecular diagnosis) were detected in 44.6% FH patients. Among 59 3'UTR variants identified, LDLR rs5742911 and PCSK9 rs17111557 were associated with molecular diagnosis of FH, whereas LDLR rs7258146 and rs7254521 and LDLRAP1 rs397860393 had an opposite effect (p < 0.05). 3´UTR variants in LDLR (rs5742911, rs7258146, rs7254521) and PCSK9 (rs17111557) disrupt interactions with several miRNAs, and more stable bindings were found with LDLR (miR-4435, miR-509-3 and miR-502) and PCSK9 (miR-4796). LDLR and PCSK9 3´UTR variants disturb miRNA:mRNA interactions that could affect gene expression and are potentially associated with molecular diagnosis of FH.

Novel Tools for Comprehensive Functional Analysis of LDLR (Low-Density Lipoprotein Receptor) Variants.

Familial hypercholesterolemia (FH) is an autosomal-dominant disorder caused mainly by substitutions in the low-density lipoprotein receptor (LDLR) gene, leading to an increased risk of premature cardiovascular diseases. Tremendous advances in sequencing techniques have resulted in the discovery of more than 3000 variants of the LDLR gene, but not all of them are clinically relevant. Therefore, functional studies of selected variants are needed for their proper classification. Here, a single-cell, kinetic, fluorescent LDL uptake assay was applied for the functional analysis of LDLR variants in a model of an LDLR-deficient human cell line. An LDLR-defective HEK293T cell line was established via a CRISPR/Cas9-mediated luciferase-puromycin knock-in. The expressing vector with the LDLR gene under the control of the regulated promoter and with a reporter gene has been designed to overproduce LDLR variants in the host cell. Moreover, an LDLR promoter-luciferase knock-in reporter system has been created in the human cell line to study transcriptional regulation of the LDLR gene, which can serve as a simple tool for screening and testing new HMG CoA reductase-inhibiting drugs for atherosclerosis therapy. The data presented here demonstrate that the obtained LDLR-deficient human cell line HEK293T-ldlrG1 and the dedicated pTetRedLDLRwt expression vector are valuable tools for studying LDL internalization and functional analysis of LDLR and its genetic variants. Using appropriate equipment, LDL uptake to a single cell can be measured in real time. Moreover, the luciferase gene knock-in downstream of the LDLR promotor allows the study of promoter regulation in response to diverse conditions or drugs. An analysis of four known LDLR variants previously classified as pathogenic and benign was performed to validate the LDLR-expressing system described herein with the dedicated LDLR-deficient human cell line, HEK293T-ldlrG1.

Novel LDLR Variant in Familial Hypercholesterolemia: NGS-Based Identification, In Silico Characterization, and Pharmacogenetic Insights.

Familial Hypercholesterolemia (FH) is a hereditary condition that causes a rise in blood cholesterol throughout a person's life. FH can result in myocardial infarction and even sudden death if not treated. FH is thought to be caused mainly by variants in the gene for the low-density lipoprotein receptor (LDLR). This study aimed to investigate the genetic variants in FH patients, verify their pathogenicity, and comprehend the relationships between genotype and phenotype. Also, review studies assessed the relationship between the LDLR null variants and the reaction to lipid-lowering therapy. The study utilised high-throughput next-generation sequencing for genetic screening of FH-associated genes and capillary sequencing for cascade screening. Furthermore, bioinformatic analysis was employed to describe the pathogenic effects of the revealed novel variant on the structural features of the corresponding RNA molecule. We studied the clinical signs of hypercholesterolemia in a Saudi family with three generations of FH. We discovered a novel frameshift variant (c.666_670dup, p.(Asp224Alafs*43) in the LDLR and a known single nucleotide variant (c.9835A > G, p.(Ser3279Gly) in the APOB gene. It is thought that the LDLR variant causes a protein to be prematurely truncated, likely through nonsense-mediated protein decay. The LDLR variant is strongly predicted to be pathogenic in accordance with ACMG guidelines and co-segregated with the FH clinical characteristics of the family. This LDLR variant exhibited severe clinical FH phenotypes and was restricted to the LDLR protein's ligand-binding domain. According to computational functional characterization, this LDLR variant was predicted to change the free energy dynamics of the RNA molecule, thereby affecting its stability. This frameshift variant is thought to eliminate important functional domains in LDLR that are required for receptor recycling and LDL particle binding. We provide insight into how FH patients with a null variant in the LDLR gene respond to lipid-lowering therapy. The findings expand the range of FH variants and assist coronary artery disease preventive efforts by improving diagnosis, understanding the genotype-phenotype relationship, prognosis, and personalised therapy for patients with FH.

Detrimental effects of PCSK9 loss-of-function in the pediatric host response to sepsis are mediated through independent influence on Angiopoietin-1

BackgroundSepsis is associated with significant mortality. Yet, there are no efficacious therapies beyond antibiotics. PCSK9 loss-of-function (LOF) and inhibition, through enhanced low-density lipoprotein receptor (LDLR) mediated endotoxin clearance, holds promise as a potential therapeutic approach among adults. In contrast, we have previously demonstrated higher mortality in the juvenile host. Given the potential pleiotropic effects of PCSK9 on the endothelium, beyond canonical effects on serum lipoproteins, both of which may influence sepsis outcomes, we sought to test the influence of PCSK9 LOF genotype on endothelial dysfunction.MethodsSecondary analyses of a prospective observational cohort of pediatric septic shock. Genetic variants of PCSK9 and LDLR genes, serum PCSK9, and lipoprotein concentrations were determined previously. Endothelial dysfunction markers were measured in day 1 serum. We conducted multivariable linear regression to test the influence of PCSK9 LOF genotype on endothelial markers, adjusted for age, complicated course, and low- and high-density lipoproteins (LDL and HDL). Causal mediation analyses to test impact of select endothelial markers on the association between PCSK9 LOF genotype and mortality. Juvenile Pcsk9 null and wildtype mice were subject to cecal slurry sepsis and endothelial markers were quantified.ResultsA total of 474 patients were included. PCSK9 LOF was associated with several markers of endothelial dysfunction, with strengthening of associations after exclusion of those homozygous for the rs688 LDLR variant that renders it insensitive to PCSK9. Serum PCSK9 was not correlated with endothelial dysfunction. PCSK9 LOF influenced concentrations of Angiopoietin-1 (Angpt-1) upon adjusting for potential confounders including lipoprotein concentrations, with false discovery adjusted p value of 0.042 and 0.013 for models that included LDL and HDL, respectively. Causal mediation analysis demonstrated that the effect of PCSK9 LOF on mortality was mediated by Angpt-1 (p = 0.0008). Murine data corroborated these results with lower Angpt-1 and higher soluble thrombomodulin among knockout mice with sepsis relative to the wildtype.ConclusionsWe present genetic and biomarker association data that suggest a potential direct role of the PCSK9-LDLR pathway on Angpt-1 in the developing host with septic shock and warrant external validation. Further, mechanistic studies on the role of PCSK9-LDLR pathway on vascular homeostasis may lead to the development of pediatric-specific sepsis therapies.Graphical abstract

In vitro assessment of the pathogenicity of the LDLR c.2160delC variant in familial hypercholesterolemia

BackgroundFamilial hypercholesterolemia (FH) is an inherited disorder with markedly elevated low-density lipoprotein cholesterol (LDL-C) and premature atherosclerotic cardiovascular disease. Although many mutations have been reported in FH, only a few have been identified as pathogenic mutations. This study aimed to confirm the pathogenicity of the LDL receptor (LDLR) c.2160delC variant in FH.MethodsIn this study, the proband and her family members were systematically investigated, and a pedigree map was drawn. High-throughput whole-exome sequencing was used to explore the variants in this family. Next, quantitative polymerase chain reaction (qPCR), western blot (WB) assays, and flow cytometry were conducted to detect the effect of the LDLR c.2160delC variant on its expression. The LDL uptake capacity and cell localization of LDLR variants were analyzed by confocal microscopy.ResultsAccording to Dutch Lipid Clinic Network (DLCN) diagnostic criteria, three FH patients were identified with the LDLR c.2160delC variant in this family. An in-silico analysis suggested that the deletion mutation at the 2160 site of LDLR causes a termination mutation. The results of qPCR and WB verified that the LDLR c.2160delC variant led to early termination of LDLR gene transcription. Furthermore, the LDLR c.2160delC variant caused LDLR to accumulate in the endoplasmic reticulum, preventing it from reaching the cell surface and internalizing LDL.ConclusionsThe LDLR c.2160delC variant is a terminating mutation that plays a pathogenic role in FH.

Identification of Novel and Known LDLR Variants Triggering Severe Familial Hypercholesterolemia in Saudi Families.

Familial hypercholesterolemia (FH) is a common illness mainly caused by variants occurring in the low-density lipoprotein receptor (LDLR) gene. FH is a leading cause of coronary artery disease. This study aims to determine genetic defect(s) in homozygous and heterozygous FH index patients and their first-degree blood relatives and understand the genotype-phenotype correlation. This study employed the genetic screening of FH-related genes by next-generation sequencing and cascade screening by capillary sequencing. We identified the presence of a novel frameshift variant [c.335_336insCGAG, p.(F114Rfs*17)] and three known missense variants [c.622G>A, p.(E208K)], [c.1474G>A, p.(D492N)], [c.1429G>A, p.(D477N)] in the LDLR gene of four unrelated Saudi families with FH. In proband 1, a nonsense variant c.1421C>G, p.(S474*) was also detected at exon 9 of the lipoprotein lipase gene. The segregation arrangement of the identified variants corresponded with the clinical characteristics. In this study, all the detected variants were confined in the ligand-binding domain and epidermal growth factor (EGF)-precursor homology domain of the LDLR protein, which portrayed severe clinical phenotypes of FH. Moreover, these LDLR variants were in a highly conserved residue of the proteins. In addition to the finding of the novel variant in the LDLR gene that extends the spectrum of variants causing FH, the results of this study also support the need for diagnostic screening and cascade genetic testing of this high-risk condition and to understand the genotype-phenotype correlation, which could lead to better prevention of coronary artery disease.

RNA Studies Demonstrate that the LDLR c.2389+4A>G Intronic Variant Causes Familial Hypercholesterolemia through an RNA Splicing Impact

Lead Author's Financial Disclosures H.Z. is an employee of Ambry Genetics. Study Funding None. Background/Synopsis Familial hypercholesterolemia (FH) is an inherited disorder characterized by high plasma levels of low-density lipoprotein cholesterol (LDL-C). Mutations in the low-density lipoprotein receptor (LDLR) gene are the most common cause of FH. However, not all alterations in LDLR are pathogenic; some represent benign genetic variation, and the clinical significance of any given variant is not always clear. Variants of uncertain significance (VUS) require additional studies to elucidate their pathogenicity. Objective/Purpose We sought to further characterize an intronic LDLR alteration originally classified as a VUS in a large family with clinical FH. Methods We performed multigene panel testing for four genes associated with FH (APOB, LDLR, LDLRAP1, and PCSK9) on the proband of a large family with a strong family history of high cholesterol and premature death; additional affected and unaffected family members were genotyped by Sanger sequencing for an identified intronic LDLR variant. The splicing impact of the LDLR variant was ascertained by RT-PCRseq performed on three affected individuals. Results Panel testing detected LDLR c.2389+4A>G in the proband. No other pathogenic variants, likely pathogenic variants, or VUSs were identified. Subsequent familial testing indicated that LDLR c.2389+4A>G cosegregates with disease. RNA studies demonstrated that this alteration causes skipping of exon 16, which is predicted to result in the in-frame deletion of 26 amino acids. This deletion removes part of the transmembrane domain and is expected to disrupt the ability of LDLR to insert into the membrane, resulting in loss of receptor function. Other pathogenic alterations impacting the same donor splice site have been shown to have a similar impact on splicing (LDLR c.2389G>T and LDLR c.2389+1G>T; Bourbon M et al. J. Med. Genet., 2009 May;46:352-7; Holla ØL et al. Mol. Genet. Metab., 2009 Apr;96:245-52). Conclusions The LDLR c.2389+4A>G intronic variant is a pathogenic mutation that results in a splice defect and cosegregates with disease. In this case, RNA and family studies resulted in a reclassification from a VUS to a pathogenic mutation and confirmed the molecular cause of the multigenerational FH. Clinical management recommendations exist for individuals with a confirmed FH diagnosis, and an accurate genetic diagnosis can improve patient outcomes through tailored treatments (Brown E et al. J. Clin. Lipidol.,2020 Jul-Aug;14:398-413). Our findings highlight the utility of familial testing and RNA studies in clarifying the classification of DNA variants. H.Z. is an employee of Ambry Genetics.

Evinacumab Markedly Reduces Low-density Lipoprotein Cholesterol in Adolescent Patients With Homozygous Familial Hypercholesterolemia†

Lead Author's Financial Disclosures Nothing to disclose. Study Funding Regeneron Pharmaceuticals, Inc. Background/Synopsis Homozygous familial hypercholesterolemia (HoFH) is characterized by elevated low-density lipoprotein cholesterol (LDL-C) and premature cardiovascular disease, underscoring the need for early and aggressive treatment. Evinacumab, an angiopoietin-like protein 3 inhibitor, is an effective LDL-C lowering drug in adult HoFH patients. Objective/Purpose The primary objective of the study is to evaluate the safety and tolerability of intravenous evinacumab 15 mg/kg every 4 weeks in adolescent patients with HoFH. Methods This is an interim analysis of an evinacumab open-label phase 3 trial (NCT03409ba744) in adolescent patients (aged 12 to <18 years) with HoFH. Patients who participated in a previous study (NCT03399786) or who were evinacumab-naive received intravenous evinacumab 15 mg/kg every 4 weeks. All patients were genotyped. Results In total, 13 patients (8 male; mean [range] age 14 [12-17] years) were treated for a mean (range) duration of 34.5 (4-61) weeks. At baseline, mean (standard deviation [SD]) LDL-C was 310.3 [97.3] mg/dL; 8 patients (61.5%) received lipoprotein apheresis. Treatment-emergent adverse events (TEAEs) occurred in 6 (46.2%) patients; no TEAEs were reported in more than 1 patient. One patient reported 2 serious adverse events, both considered unrelated to study drug. LDL-C data were available for 9 patients at week 24. Overall, evinacumab reduced mean LDL-C by 52.4% (mean [SD], 183.4 [101.6] mg/dL; Figure) from baseline to week 24. In patients with null-null (n=4) and non-null (n=5) LDL-receptor variants, evinacumab reduced mean LDL-C levels by 67.2% and 40.6%, respectively. Conclusions In this small sample of adolescent patients with HoFH, evinacumab markedly reduced LDL-C irrespective of genotype or background treatment in patients with HoFH. Evinacumab was generally well-tolerated with few TEAEs. Nothing to disclose.

MLb-LDLr: A Machine Learning Model for Predicting the Pathogenicity of LDLr Missense Variants

Untreated familial hypercholesterolemia (FH) leads to atherosclerosis and early cardiovascular disease. Mutations in the low-density lipoprotein receptor (LDLr) gene constitute the major cause of FH, and the high number of mutations already described in the LDLr makes necessary cascade screening or invitro functional characterization to provide a definitive diagnosis. Implementation of high-predicting capacity software constitutes a valuable approach for assessing pathogenicity of LDLr variants to help in the early diagnosis and management of FH disease. This work provides a reliable machine learning model to accurately predict the pathogenicity of LDLr missense variants with specificity of 92.5% and sensitivity of 91.6%.

The LDLR c.501C>A is a disease-causing variant in familial hypercholesterolemia

BackgroundAs an autosomal dominant disorder, familial hypercholesterolemia (FH) is mainly attributed to disease-causing variants in the low-density lipoprotein receptor (LDLR) gene. The aim of this study was to explore the molecular mechanism of LDLR c.501C>A variant in FH and assess the efficacy of proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitor treatment for FH patients.MethodsThe whole-exome sequencing was performed on two families to identify disease-causing variants, which were verified by Sanger sequencing. The function of LDLR variant was further explored in HEK293 cells by Western Blot and confocal microscopy. Besides, the therapeutic effects of PCSK9 inhibitor treatment for two probands were assessed for 3 months.ResultsAll members of the two families with the LDLR c.501C>A variant showed high levels of LDLC. The relationship between the clinical phenotype and LDLR variants was confirmed in the current study. Both in silico and in vitro analyses showed that LDLR c.501C>A variant decreased LDLR expression and LDL uptake. PCSK9 inhibitor treatment lowered the lipid level in proband 1 by 24.91%. However, the treatment was ineffective for proband 2. A follow-up study revealed that the PCSK9 inhibitor treatment had low ability of lipid-lowering effect in the patients.ConclusionsLDLR c.501C>A variant might be pathogenic for FH. The PCSK9 inhibitor therapy is not a highly effective option for treatment of FH patients with LDLR c.501C>A variant.

Functional analysis of LDLR genetic variants identified in hypercholesterolemic patients in BRAZIL, using CRISPR/CAS9

Background and Aims: Introduction: The familial hypercholesterolemia (FH) is one of the main causes of cardiovascular diseases, and it is mainly caused by genetic variants at the low-density lipoprotein receptor (LDLR). Although ultrasequencing technology has allowed the identification of several genetic variants, few of them was functional analyzed. The CRISPR/Cas9 tool promotes precise genetic editing and allows the creation of experimental models, therefore contributing to the functional validation process. Aim: To use the CRISPR/Cas9 tool to perform in vitro functional analysis of LDLR variants identified in FH patients.

Diet-Responsive Hypercholesterolemia With Cardiofaciocutaneous Syndrome Type 3

Background: Molecular basis of diet responsive hypercholesterolemia remains unclear. We report diet-responsive severe hypercholesterolemia in a young female with cardiofaciocutaneous syndrome type 3 (CFC3) due to a heterozygous pathogenic MAP2K1 variant, suggesting a role of common MAPK variants in LDL-cholesterol (LDL-C) response to diet. Clinical case: A 3-year-old Caucasian female with CFC3 (macrocephaly, frontal bossing, wide nasal root with depressed bridge, anteverted nares, low set fleshy ears, congenital pulmonic valve stenosis, postnatal growth deficiency, hypotonia, and neurocognitive impairment) due to a de novo heterozygous c.389A>G, p.Tyr130Cys pathogenic variant in MAP2K1, presented with extremely elevated serum total cholesterol of 446 mg/dL, triglycerides of 239 mg/dL, HDL-cholesterol of 53 mg/dL, LDL-C of 335 mg/dL (normal range < 110 mg/dL) and serum apolipoprotein B level 219 mg/dL (normal range < 90 mg/dL). Her LDL-C was 252 mg/dL a year ago and 215 mg/dL one month prior to presentation. Reducing total dietary fat to 20–25% of total energy and saturated fat to <6% of total energy over the next 4 months lowered LDL-C to 104 mg/dL. However, her weight decreased by 0.5 kg and liberalization of fat intake again increased LDL-C to 222 mg/dL. Her father has mildly elevated LDL-C of 160 mg/dL and her mother had normal LDL-C of 80 mg/dL. Her plasma phytosterol levels were normal and she had ApoE3/E3 genotype. Targeted genetic testing of the patient and parents showed a benign heterozygous LDL receptor (LDLR) variant c.2242G>A; p.Asp748Asn, (Minor allele frequency 0.00008) in the patient and her father. Whole exome sequencing of the patient and both parents showed no known disease-causing variants in LDLR, APOB, PCSK9, LDLRAP1, APOE, STAP1, LIPA, ABCG5, ABCG8 and other known hyperlipidemia-related genes. There are no previous reports of hypercholesterolemia in patients with CFC3. MAP2K1 stimulates various MAP kinases upon wide variety of extra- and intracellular signal and is involved in cell proliferation, differentiation, transcription regulation and development. Previous studies of the relationship between p42/44MAPK activation and LDLR expression in human hepatoma HepG2-derived cell line showed that that activation of the Raf-1/MEK/p42/44MAPK cascade induces LDLR expression and modulation of the Raf-1 kinase signal strength can determine LDLR expression levels. Thus, extent of MAPK activation can alter signaling of LDLR, resulting in hypercholesterolemia. Conclusion: Our case report suggests that MAP2K1 may play a significant role in LDLR signaling, and some MAP2K1 variants may be associated with diet-responsive hypercholesterolemia. Larger studies are required to assess dietary response to LDL-C in subjects with MAP2K1 variants.

High-throughput microscopy profiling of LDLR variants

Background and Aims: Mutations in the Low Density Lipoprotein Receptor (LDLR) gene are the major cause of familial hypercholesterolaemia (FH), with over 2600 variants described. However, less than 15% of the LDLR variants identified in clinical FH patients have functional evidences to prove their pathogenicity. The aim of the present work is to stablish a quantitative high-throughput in vitro microscopy approach to functionally characterize rare LDLR variants.

Endoplasmic reticulum stress induced by class 2 LDLR variants

Background and Aims: Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the gene encoding the low-density lipoprotein receptor (LDLR). The majority of LDLR pathogenic variants are completely or partily retained in the endoplasmatic reticulum (ER). If these variants are not correctly processed for their elimination, the homeostasis of the ER can be altered by a sustained LDLR accumulation. This situation could lead to ER stress, a condition that contribute to hepatic injury. The aim of the present work has been to asses if c.97C>T, c.971delG and c.892delA LDLR variants, previously described in homozygous FH patients, induce ER estress.

Genetic associations between serum low LDL-cholesterol levels and variants in LDLR, APOB, PCSK9 and LDLRAP1 in African populations

Non-communicable diseases, including cardiovascular diseases (CVDs), are increasing in African populations. High serum low density lipoprotein cholesterol (LDL-cholesterol) levels are a known risk factor for CVDs in European populations, but the link remains poorly understood among Africans. This study investigated the associations between serum LDL-cholesterol levels and selected variants in the low density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9) and low density lipoprotein receptor adaptor protein 1 (LDLRAP1) genes in some selected African populations. Nineteen SNPs were selected from publicly available African whole genome sequence data based on functional prediction and allele frequency. SNPs were genotyped in 1000 participants from the AWI-Gen, study selected from the extremes of LDL-cholesterol level distribution (500 with LDL-cholesterol>3.5 mmol/L and 500 with LDL-cholesterol<1.1 mmol/L). The minor alleles at five of the six associated SNPs were significantly associated (P<0.05) with lower LDL-cholesterol levels: LDLRAP1 rs12071264 (OR 0.56, 95% CI: 0.39–0.75, P = 2.73x10-4) and rs35910270 (OR 0.78, 95% CI: 0.64–0.94, P = 0.008); APOB rs6752026 (OR 0. 55, 95% CI: 0.41–0.72, P = 2.82x10-5); LDLR: rs72568855 (OR 0.47, 95% CI: 0.27–0.82, P = 0.008); and PCSK9 rs45613943 (OR = 0.72, 95% CI: 0.58–0.88, P = 0.001). The minor allele of the sixth variant was associated with higher LDL-cholesterol levels: APOB rs679899 (OR 1.41, 95% CI: 1.06–1.86, P = 0.016). A replication analysis in the Africa America Diabetes Mellitus (AADM) study found the PCSK9 variant to be significantly associated with low LDL-cholesterol levels (Beta = -0.10). Since Africans generally have lower LDL-cholesterol levels, these LDL-cholesterol associated variants may be involved in adaptation due to unique gene-environment interactions. In conclusion, using a limited number of potentially functional variants in four genes, we identified significant associations with lower LDL-cholesterol levels in sub-Saharan Africans.