Analysis of sequence variations in low-density lipoprotein receptor gene among Malaysian patients with familial hypercholesterolemia

Development of DNA-Based Lateral Flow Assay for Detection of LDLR Gene Mutation for Familial Hypercholesterolemia

Background

The techniques for detecting single nucleotide polymorphisms (SNP) require lengthy and complex experimental procedures and expensive instruments that may only be available in some laboratories. Thus, a deoxyribonucleic acid (DNA)-based lateral flow assay (LFA) was developed as a point-of-care test (POCT) diagnostic tool for genotyping. In this study, single nucleotide variation (E101K) in the low-density lipoprotein receptor (LDLR) gene leading to familial hypercholesterolemia (FH) was chosen as a model.

Methods

Hypercholesterolemic individuals (n = 103) were selected from the Malaysian Cohort project (UKM Medical Molecular Biology Institute) while the control samples were selected from the Biobank (UKM Medical Molecular Biology Institute). The DNA samples were isolated from whole blood. Polymerase chain reaction (PCR) amplification process was performed using bifunctional labelled primers specifically designed to correspond to the variant that differentiates wild-type and mutant DNA for visual detection on LFA. The variant was confirmed using Sanger sequencing, and the sensitivity and specificity of the LFA detection method were validated using the Agena MassARRAY® technique.

Results

Out of 103 hypercholesterolemic individuals, 5 individuals (4.8%) tested positive for E101K, LDLR mutation and the rest, including healthy control individuals, tested negative. This result was concordant with Sanger sequencing and Agena MassARRAY®. These five individuals could be classified as Definite FH, as the DNA diagnosis was confirmed. The sensitivity and specificity of the variant detection by LFA is 100% compared to results using the genotyping method using Agena MassARRAY®.

Conclusion

The developed LFA can potentially be used in the POC setting for detecting the E101K variant in the LDLR gene. This LFA can also be used to screen family members with E101K variant in the LDLR gene and is applicable for other SNP's detection.

Reducing Premature Coronary Artery Disease in Malaysia by Early Identification of Familial Hypercholesterolemia Using the Familial Hypercholesterolemia Case Ascertainment Tool (FAMCAT): Protocol for a Mixed Methods Evaluation Study

BACKGROUND

Familial hypercholesterolemia (FH) is predominantly caused by mutations in the 4 FH candidate genes (FHCGs), namely, low-density lipoprotein receptor (LDLR), apolipoprotein B-100 (APOB-100), proprotein convertase subtilisin/kexin type 9 (PCSK9), and the LDL receptor adaptor protein 1 (LDLRAP1). It is characterized by elevated low-density lipoprotein cholesterol (LDL-c) levels leading to premature coronary artery disease. FH can be clinically diagnosed using established clinical criteria, namely, Simon Broome (SB) and Dutch Lipid Clinic Criteria (DLCC), and can be identified using the Familial Hypercholesterolemia Case Ascertainment Tool (FAMCAT), a primary care screening tool.

OBJECTIVE

This study aims to (1) compare the detection rate of genetically confirmed FH and diagnostic accuracy between the FAMCAT, SB, and DLCC in the Malaysian primary care setting; (2) identify the genetic mutation profiles, including novel variants, in individuals with suspected FH in primary care; (3) explore the experience, concern, and expectation of individuals with suspected FH who have undergone genetic testing in primary care; and (4) evaluate the clinical utility of a web-based FH Identification Tool that includes the FAMCAT, SB, and DLCC in the Malaysian primary care setting.

METHODS

This is a mixed methods evaluation study conducted in 11 Ministry of Health primary care clinics located at the central administrative region of Malaysia. In Work stream 1, the diagnostic accuracy study design is used to compare the detection rate and diagnostic accuracy of the FAMCAT, SB, and DLCC against molecular diagnosis as the gold standard. In Work stream 2, the targeted next-generation sequencing of the 4 FHCGs is used to identify the genetic mutation profiles among individuals with suspected FH. In Work stream 3a, a qualitative semistructured interview methodology is used to explore the experience, concern, and expectation of individuals with suspected FH who have undergone genetic testing. Lastly, in Work stream 3b, a qualitative real-time observation of primary care physicians using the "think-aloud" methodology is applied to evaluate the clinical utility of a web-based FH Identification Tool.

RESULTS

The recruitment for Work stream 1, and blood sampling and genetic analysis for Work stream 2 were completed in February 2023. Data collection for Work stream 3 was completed in March 2023. Data analysis for Work streams 1, 2, 3a, and 3b is projected to be completed by June 2023, with the results of this study anticipated to be published by December 2023.

CONCLUSIONS

This study will provide evidence on which clinical diagnostic criterion is the best to detect FH in the Malaysian primary care setting. The full spectrum of genetic mutations in the FHCGs including novel pathogenic variants will be identified. Patients' perspectives while undergoing genetic testing and the primary care physicians experience in utilizing the web-based tool will be established. These findings will have tremendous impact on the management of patients with FH in primary care and subsequently reduce their risk of premature coronary artery disease.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/47911.

Rani ZZ, Sulaiman SA, Chow YP, Abdullah N, Ahmad N, Ismail N, Abdul Jalal N, Kamaruddin MA, Saperi AA, Jamal R. Hypercholesterolemia in the Malaysian Cohort Participants: Genetic and Non-Genetic Risk Factors

Hypercholesterolemia was prevalent in 44.9% of The Malaysian Cohort participants, of which 51% were Malay. This study aimed to identify the variants involved in hypercholesterolemia among Malays and to determine the association between genetic and non-genetic risk factors. This nested case–control study included 25 Malay participants with the highest low-density lipoprotein cholesterol (LDL-C, >4.9 mmol/L) and total cholesterol (TC, >7.5 mmol/L) and 25 participants with the lowest LDL-C/TC. Genomic DNA was extracted, and whole-exome sequencing was performed using the Ion ProtonTM system. All variants were annotated, filtered, and cross-referenced against publicly available databases. Forty-five selected variants were genotyped in 677 TMC Malay participants using the MassARRAY® System. The association between genetic and non-genetic risk factors was determined using logistic regression analysis. Age, fasting blood glucose, tobacco use, and family history of hyperlipidemia were significantly associated with hypercholesterolemia. Participants with the novel OSBPL7 (oxysterol-binding protein-like 7) c.651_652del variant had 17 times higher odds for hypercholesterolemia. Type 2 diabetes patients on medication and those with PCSK9 (proprotein convertase subtilisin/kexin type 9) rs151193009 had low odds for hypercholesterolemia. Genetic predisposition can interact with non-genetic factors to increase hypercholesterolemia risk in Malaysian Malays.

PCSK9 Inhibitors Reduce PCSK9 and Early Atherogenic Biomarkers in Stimulated Human Coronary Artery Endothelial Cells

Despite reports on the efficacy of proprotein convertase subtilisin-Kexin type 9 (PCSK9) inhibitors as a potent lipid-lowering agent in various large-scale clinical trials, the anti-atherogenic properties of PCSK9 inhibitors in reducing PCSK9 and atherogenesis biomarkers via the NF-ĸB and eNOS pathway has yet to be established. This study aimed to investigate the effects of PCSK9 inhibitors on PCSK9, targeted early atherogenesis biomarkers, and monocyte binding in stimulated human coronary artery endothelial cells (HCAEC). HCAEC were stimulated with lipopolysaccharides (LPS) and incubated with evolocumab and alirocumab. The protein and gene expression of PCSK9, interleukin-6 (IL-6), E-selectin, intercellular adhesion molecule 1 (ICAM-1), nuclear factor kappa B (NF-ĸB) p65, and endothelial nitric oxide synthase (eNOS) were measured using ELISA and QuantiGene plex, respectively. The binding of U937 monocytes to endothelial cell capacity was measured by the Rose Bengal method. The anti-atherogenic effects of evolocumab and alirocumab were contributed to by the downregulation of PCSK9, early atherogenesis biomarkers, and the significant inhibition of monocyte adhesion to the endothelial cells via the NF-ĸB and eNOS pathways. These suggest the beyond cholesterol-lowering beneficial effects of PCSK9 inhibitors in impeding atherogenesis during the initial phase of atherosclerotic plaque development, hence their potential role in preventing atherosclerosis-related complications.

Low density lipoprotein receptor endocytosis in cardiovascular disease and the factors affecting LDL levels

Cardiovascular disease (CVD) is the one of major global health issues with approximately 30% of the mortality reported in the mid-income population. Low-density lipoprotein (LDL) plays a crucial role in development of CVD. High LDL along with others forms a plaque and blocks arteries, resulting in CVD. The present chapter deals with the mechanism of receptor-mediated endocytosis of LDL and its management by drugs such as statins and PCSK9 inhibitors along with dietary supplementation for health improvements.

Genetic Spectrum of Familial Hypercholesterolaemia in the Malaysian Community: Identification of Pathogenic Gene Variants Using Targeted Next-Generation Sequencing

Familial hypercholesterolaemia (FH) is caused by mutations in lipid metabolism genes, predominantly in low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin-type 9 (PCSK9) and LDL receptor adaptor protein 1 (LDLRAP1). The prevalence of genetically confirmed FH and the detection rate of pathogenic variants (PV) amongst clinically diagnosed patients is not well established. Targeted next-generation sequencing of LDLR, APOB, PCSK9 and LDLRAP1 was performed on 372 clinically diagnosed Malaysian FH subjects. Out of 361 variants identified, 40 of them were PV (18 = LDLR, 15 = APOB, 5 = PCSK9 and 2 = LDLRAP1). The majority of the PV were LDLR and APOB, where the frequency of both PV were almost similar. About 39% of clinically diagnosed FH have PV in PCSK9 alone and two novel variants of PCSK9 were identified in this study, which have not been described in Malaysia and globally. The prevalence of genetically confirmed potential FH in the community was 1:427, with a detection rate of PV at 0.2% (12/5130). About one-fourth of clinically diagnosed FH in the Malaysian community can be genetically confirmed. The detection rate of genetic confirmation is similar between potential and possible FH groups, suggesting a need for genetic confirmation in index cases from both groups. Clinical and genetic confirmation of FH index cases in the community may enhance the early detection of affected family members through family cascade screening.

Development of an Optimized Tetra-Amplification Refractory Mutation System PCR for Detection of 12 Pathogenic Familial Hypercholesterolemia Variants in the Asian Population

Early detection of genetic diseases such as familial hypercholesterolemia (FH), and the confirmation of related pathogenic variants, are crucial in reducing the risk for premature coronary artery disease. Currently, next-generation sequencing is used for detecting FH-related candidate genes but is expensive and time-consuming. There is a lack of kits suitable for the detection of the common FH-related variants in the Asia-Pacific region. Thus, this study addressed that need with the development of an optimized tetra-amplification mutation system (T-ARMS) PCR-based assay for the detection of 12 pathogenic variants of FH in the Asian population. The two important parameters for T-ARMS PCR assay performance-annealing temperature and the ratio of outer/inner primer concentrations-were optimized in this study. The optimal annealing temperature of all 12 T-ARMS PCR reactions was 64.6°C. The ideal ratios of outer/inner primer concentrations with each pathogenic variant were: A1, 1:2; A2, 1:4; L1, 1:10; L2, 1:1; L3, 1:2; L4, 1:8; L5, 1:1; L6, 1:2; L7, 1:8; L8, 1:8; L9, 1:2; and L10, 1:8. The lowest limit of detection using DNA extracted from patients was 0.1 ng. The present article highlights the beneficial findings on T-ARMS PCR as part of the development of a PCR-based detection kit for use in detecting FH in economically developing countries in Asia with a greater prevalence of FH.

Screening of PCSK9 and LDLR genetic variants in Familial Hypercholesterolemia (FH) patients in India

Familial Hypercholesterolemia (FH) is an autosomal, dominant, inherited disorder characterized by severely elevated LDL-cholesterol (LDL-C) levels with high risk for Coronary Artery Disease (CAD). There are limited genetic studies especially on genes other than Low Density Lipoprotein receptor (LDLR) conducted in Indian population. Thus, our aim was to screen the entire Proprotein Convertase Subtilisin/Kexin type 9 gene (PCSK9) gene & hotspot exons 3, 4 and 9 of LDLR gene in FH cases and controls. 50 FH cases were categorized into definite, probable and possible cases according to Dutch Lipid Network Criteria (DLNC) who were gender matched with 50 healthy controls. All 12 exons of PCSK9, and hotspot exons 3, 4 & 9 of LDLR gene were screened through High Resolution Melt (HRM) curve analysis. Enzyme linked immunosorbent assay was performed to measure circulating PCSK9 levels. Total cholesterol and LDL-C were significantly high in all three groups of cases. Total 8 nonpathogenic variants in exon 1, 5, 7 and 9 of the PCSK9 gene were detected. In LDLR gene, 3 known pathogenic and 1 benign variant were found in exon 3 & 4. In FH cases, PCSK9 levels were significantly high compared to controls (P = 0.0001), and were directly correlated to LDL-C (P = 0.0001) and Total Cholesterol (P = 0.0001). Our study is first to screen the entire PCSK9 gene in western part of India. Since no pathogenic variants were identified, it is possible that PCSK9 variants are clinically less relevant. However, 3 known pathogenic variants were found in the LDLR gene. These findings support our understanding of the genetic spectrum of FH in India.

Molecular Genetic Approach and Evaluation of Cardiovascular Events in Patients with Clinical Familial Hypercholesterolemia Phenotype from Romania

This study identifies the genetic background of familial hypercholesterolemia (FH) patients in Romania and evaluates the association between mutations and cardiovascular events. We performed a prospective observational study of 61 patients with a clinical diagnosis of FH selected based on Dutch Lipid Clinic Network (DLCN) and Simon Broome score between 2017 and 2020. Two techniques were used to identify mutations: multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing. The mutation rate was 37.7%, i.e., 23 patients with mutations were identified, of which 7 subjects had pathogenic mutations and 16 had polymorphisms. Moreover, 10 variants of the low-density lipoprotein receptor (LDLR) gene were identified in 22 patients, i.e., one variant of the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene in six patients, and one variant of the apolipoprotein B (APOB) gene in three patients. Of the LDLR gene variants, four were LDLR pathogenic mutations (c.81C > G, c.502G > A, c.1618G > A mutations in exon 2, exon 4, exon 11, and exon 13–15 duplication). The PCSK9 and APOB gene variants were benign mutations. The pathogenic LDLR mutations were significant predictors of the new cardiovascular events, and the time interval for new cardiovascular events occurrence was significantly decreased, compared to FH patients without mutations. In total, 12 variants were identified, with four pathogenic variants identified in the LDLR gene, whereas 62.3% of the study population displayed no pathological mutations.

Familial hypercholesterolemia in Southeast and East Asia

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Even though at least a quarter of the world's FH population lives in Southeast and East Asia, there are substantial gaps in knowledge regarding the epidemiology of FH due to low awareness, the absence of national screening programs, and limited availability of genetic testing.

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We discuss the most recent and relevant information available related to diagnostic criteria, prevalence, awareness, clinical characteristics, genetic epidemiology, and treatment in the FH population of Southeast and East Asia.

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Increasing awareness and improving the diagnosis and management of FH will reduce the burden of premature CHD in these regions of the world.

Familial hypercholesterolemia (FH) is a relatively common autosomal dominant disorder associated with a significantly increased risk of coronary heart disease (CHD). Most (~85–90%) cases are due to pathogenic variants in the LDL-receptor gene (LDLR), while the remaining are due to pathogenic variants in the apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes, though the proportion may vary depending on geographic location. Even though at least a quarter of the world's FH population lives in Southeast and East Asia, there are substantial gaps in knowledge regarding the epidemiology of FH due to low awareness, the absence of national screening programs, and limited availability of genetic testing. In this review, we discuss the most recent and relevant information available related to diagnostic criteria, prevalence, awareness, clinical characteristics, genetic epidemiology, and treatment in the FH population of Southeast and East Asia. Increasing awareness and improving the diagnosis and management of FH will reduce the burden of premature CHD in these regions of the world.

Genetic Diagnosis of Familial Hypercholesterolemia in Asia

Familial hypercholesterolemia (FH) is a common genetic disease with an incidence of about 1 in 200-500 individuals. Genetic mutations markedly elevate low-density lipoprotein cholesterol and atherosclerotic cardiovascular disease (ASCVD) in FH patients. With advances in clinical diagnosis and genetic testing, more genetic mutations have been detected, including those in low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9), and so on. Globally, most FH patients remain undiagnosed, untreated, or inappropriately treated. Recently, there was a Global Call to Action by the Global Familial Hypercholesterolemia Community to reduce the health burden of FH. Asia, despite being the most populous continent with half of the global population, has low FH detection rates compared to Western countries. Therefore, we aimed to review the current status of FH genetic diagnosis in Asia to understand the gaps in FH diagnosis and management in this region.

LDLR Gene Polymorphisms (rs5925 and rs1529729) Are Associated with Susceptibility to Coronary Artery Disease in a South Indian Population

Cardiovascular diseases (CVD) are a major cause of death in India and worldwide. Atherosclerosis is caused by the interaction of environmental and genetic factors. Hypercholesterolemia is an example of a classical risk factor for CVD. The low-density lipoprotein receptor (LDLR) is one of the regulating mechanisms the liver uses for cholesterol homeostasis. Gene variations in the LDLR have been reported to cause hypercholesterolemia and consequently CVD. We investigated the association of polymorphisms in the LDLR (rs5925 and rs1529729) with coronary artery disease (CAD) in 200 coronary artery disease patients and 200 matched healthy controls using allele-specific PCR (AS-PCR). The results indicated that the CT genotype of the rs1529729 polymorphism was associated a decreased susceptibility to CAD with an odds ratio (OR) = 0.42 (95% confidence interval (CI), 0.23–0.77), risk ratio (RR) = 0.59 (0.39–0.89), P = 0.0047. The TT genotype of the rs1529729 polymorphism was also associated with decreased susceptibility to CAD with an OR = 0.19 (95% CI, 0.076–0.47), RR = 0.57 (0.47–0.69), P = 0.0003. The GA genotype of the rs5925 polymorphism was associated with decreased susceptibility to CAD with an OR = 0.45 (95% CI, 0.27–0.75), RR = 0.65 (0.47–0.88), P = 0.002. We concluded that the CT and TT genotypes of the rs1529729 polymorphism and the GA genotype of the rs5925 polymorphism are probably associated with decreased susceptibility to CAD. The simplicity of AS-PCR makes it particularly suitable for the rapid, large-scale screening of gene variabilities in the LDLR. AS-PCR could provide significant benefits in clinical applications with its ability to amplify a lower quantity of samples in a cost-saving manner. Nevertheless, these findings need to be validated in well-designed studies with larger sample sizes and in different populations.

Heterozygous familial hypercholesterolaemia in a pair of identical twins: a case report and updated review

BACKGROUND

Familial hypercholesterolaemia (FH) is the most common inherited metabolic disease with an autosomal dominant mode of inheritance. It is characterised by raised serum levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-c), leading to premature coronary artery disease. Children with FH are subjected to early and enhanced atherosclerosis, leading to greater risk of coronary events, including premature coronary artery disease. To the best of our knowledge, this is the first report of a pair of monochorionic diamniotic identical twins with a diagnosis of heterozygous FH, resulting from mutations in both LDLR and ABCG8 genes.

CASE PRESENTATION

This is a rare case of a pair of 8-year-old monochorionic diamniotic identical twin, who on family cascade screening were diagnosed as definite FH, according to the Dutch Lipid Clinic Criteria (DLCC) with a score of 10. There were no lipid stigmata noted. Baseline lipid profiles revealed severe hypercholesterolaemia, (TC = 10.5 mmol/L, 10.6 mmol/L; LDL-c = 8.8 mmol/L, 8.6 mmol/L respectively). Their father is the index case who initially presented with premature CAD, and subsequently diagnosed as FH. Family cascade screening identified clinical FH in other family members including their paternal grandfather who also had premature CAD, and another elder brother, aged 10 years. Genetic analysis by targeted next-generation sequencing using MiSeq platform (Illumina) was performed to detect mutations in LDLR, APOB100, PCSK9, ABCG5, ABCG8, APOE and LDLRAP1 genes. Results revealed that the twin, their elder brother, father and grandfather are heterozygous for a missense mutation (c.530C > T) in LDLR that was previously reported as a pathogenic mutation. In addition, the twin has heterozygous ABCG8 gene mutation (c.55G > C). Their eldest brother aged 12 years and their mother both had normal lipid profiles with absence of LDLR gene mutation.

CONCLUSION

A rare case of Asian monochorionic diamniotic identical twin, with clinically diagnosed and molecularly confirmed heterozygous FH, due to LDLR and ABCG8 gene mutations have been reported. Childhood FH may not present with the classical physical manifestations including the pathognomonic lipid stigmata as in adults. Therefore, childhood FH can be diagnosed early using a combination of clinical criteria and molecular analyses.

Genetic diagnosis of familial hypercholesterolemia is associated with a premature and high coronary heart disease risk

BACKGROUND

Familial hypercholesterolemia (FH) is a common autosomal dominant disease associated with premature coronary heart disease (CHD). Studies tend to show that patients with FH associated with an identified mutation (mutation+ FH) are at higher risk than patients without an identified mutation (mutation- FH). We compared the clinical and biological profile and the risk of CHD in patients with mutation+ FH and mutation- FH.

HYPOTHESIS

In addition to LDL-C, a pathogenic mutation predicts premature CHD in FH.

METHODS

We successively included all patients with suspected FH (LDL-C > 190 mg/dL if age > 18 years; LDL-C > 160 mg/dL if age < 18 years) and compared patients with a pathogenic mutation with those without an identified pathogenic mutation.

RESULTS

We studied 179 patients with mutation+ FH and 147 with mutation- FH. The mean age was 44 (± 18) years. The lipid profile was more atherogenic in those with mutation+ FH, who had higher LDL-C (254 ± 69 mg/dL vs 218 ± 35 mg/dL; P < 0.01) and lower HDL-C (53 ± 14 mg/dL vs 58 ± 17 mg/dL; P < 0.01). Despite the more atherogenic nonlipid cardiovascular profile of patients with mutation- FH, the age of CHD onset was earlier in patients with mutation+ FH (48 vs 56 years; P = 0.026). After multiple adjustment, the presence of a positive mutation was significantly associated with premature CHD (OR: 3.0, 95% CI: 1.38-6.55, P < 0.01).

CONCLUSIONS

Patients with mutation+ FH have a more atherogenic lipid profile and a 3-fold higher risk of premature CHD, as well as earlier onset of CHD, than patients with mutation- FH.

Genetic Analysis of Iranian Patients with Familial Hypercholesterolemia

Background:

Familial hypercholesterolemia (FH) is a frequent autosomal dominant disorder of lipoprotein metabolism. This disorder is generally caused by mutations in low-density lipoprotein receptor (LDLR), apolipoprotein B 100 (APOB), and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes. In the present study, we aimed at identifying the common LDLR and APOB gene mutations in an Iranian population.

Methods:

Eighty unrelated Iranian patients with FH entered the study, based on Simon Broome diagnostic criteria. All samples were screened for two common APOB gene mutations, including R3500Q and R3500W, by the means of ARMS-PCR and PCR- RFLP assays, respectively. In addition, exons 3, 4, 9, and 10 of LDLR gene were sequenced in all patients.

Results:

A novel mutation in exon 3 (C95W) and a previously described mutation in exon 4 (D139H) of LDLR gene were found. Three previously reported polymorphisms in LDLR gene as well as three novel polymorphisms were detected in the patients. However, in the studied population, no common mutations were observed in APOB gene.

Conclusion:

The results of our study imply that the genetic basis of FH in Iranian patients is different from other populations.

Molecular testing for familial hypercholesterolaemia-associated mutations in a UK-based cohort: development of an NGS-based method and comparison with multiplex polymerase chain reaction and oligonucleotide arrays

Background Detection of disease-associated mutations in patients with familial hypercholesterolaemia is crucial for early interventions to reduce risk of cardiovascular disease. Screening for these mutations represents a methodological challenge since more than 1200 different causal mutations in the low-density lipoprotein receptor has been identified. A number of methodological approaches have been developed for screening by clinical diagnostic laboratories. Methods Using primers targeting, the low-density lipoprotein receptor, apolipoprotein B, and proprotein convertase subtilisin/kexin type 9, we developed a novel Ion Torrent-based targeted re-sequencing method. We validated this in a West Midlands-UK small cohort of 58 patients screened in parallel with other mutation-targeting methods, such as multiplex polymerase chain reaction (Elucigene FH20), oligonucleotide arrays (Randox familial hypercholesterolaemia array) or the Illumina next-generation sequencing platform. Results In this small cohort, the next-generation sequencing method achieved excellent analytical performance characteristics and showed 100% and 89% concordance with the Randox array and the Elucigene FH20 assay. Investigation of the discrepant results identified two cases of mutation misclassification of the Elucigene FH20 multiplex polymerase chain reaction assay. A number of novel mutations not previously reported were also identified by the next-generation sequencing method. Conclusions Ion Torrent-based next-generation sequencing can deliver a suitable alternative for the molecular investigation of familial hypercholesterolaemia patients, especially when comprehensive mutation screening for rare or unknown mutations is required.

Premature coronary heart disease and autosomal dominant hypercholesterolemia: Increased risk in women with LDLR mutations

BACKGROUND

For patients with autosomal dominant hypercholesterolemia (ADH), it remains unclear whether differences exist in the risk of premature coronary heart disease (CHD) between patients with confirmed mutations in low-density lipoprotein receptor (LDLR) vs those without detectable mutations.

OBJECTIVE

This study sought to assess the risk of premature CHD in ADH patients with mutations in LDLR (referred to as familial hypercholesterolemia [FH]) vs those without detectable mutations (unexplained ADH), stratified by sex.

METHODS

Comparative study of premature CHD in a multiethnic cohort of 111 men and 165 women meeting adult Simon-Broome criteria for ADH.

RESULTS

Women with FH (n = 51) had an increased risk of premature CHD compared with unexplained ADH women (n = 111; hazard ratio [HR], 2.74; 95% confidence interval, 1.40-5.34; P = .003) even after adjustment for lipid levels and traditional CHD risk factors (HR, 2.53 [1.10-5.83]; P = .005). Men with FH (n = 42), in contrast, had a similar risk of premature CHD when compared with unexplained ADH men (n = 66; unadjusted: HR, 1.48 [0.84-2.63]; P = .18; adjusted: HR, 1.04 [0.46-2.37]; P = .72). To address whether mutation status provides additional information beyond LDL-cholesterol level, we analyzed premature CHD risk for FH vs unexplained ADH at various percentiles of LDL-cholesterol: the risk ratios were significant for women at 25th percentile (HR, 4.90 [1.69-14.19]) and 50th percentile (HR, 3.44 [1.42-8.32]) but not at 75th percentile (HR, 1.99 [0.95-4.17]), and were not significant for men at any percentile.

CONCLUSIONS

Our findings suggest that genetic confirmation of ADH may be important to identify patient's risk of CHD, especially for female LDLR mutation carriers.

Familial hypercholesterolemia: Molecular characterization of possible cases from the Azores Islands (Portugal)

Familial hypercholesterolemia (FH) is an autosomal dominant disorder of the cholesterol metabolism, which constitutes a risk factor for coronary arterial disease (CAD). In the Azores Islands (Portugal), where mortality from CAD doubles its rate comparatively to the rest of the country and where a high frequency of dyslipidemia has been reported, the prevalence and distribution of FH remain unknown. The molecular characterization of a group of 33 possible cases of FH of Azorean background was undertaken in this study. A DNA array was initially used to search mutations in the LDLR, APOB and PCSK9 loci in 10 unrelated possible cases of FH. No mutations were detected in the array; after sequencing the full LDLR gene, 18 variants were identified, corresponding to two missense (c.806G > A; c.1171G > A) and sixteen synonymous alterations. Six of the synonymous variants which are consistently described in the literature as associated with altered cholesterol levels were used to build haplotypes. The most frequent haplotype corresponded to TTCGCC (45%), a “risk” haplotype, formed exclusively by alleles that were reported to increase cholesterol levels. Some of the variants detected in the full sequencing of the LDLR gene fell within the ligand-binding domain of this gene, defined by exons 2 to 6. To add information as to the role of such variants, these exons were sequenced in the remaining 23 possible FH cases. Two missense alterations (c.185C > T; c.806G > A) were found in this subset of possible FH cases. The missense alteration c.185C > T, identified in one individual, is novel for the Portuguese population. In silico analysis was not conclusive for this alteration, whose role will have to be further investigated. This study represents the first approach to the establishment of the mutational profile of FH in the Azores Islands.

Molecular description of familial defective APOB-100 in Malaysia

Familial ligand-defective apolipoprotein B-100 is characterized by elevated plasma low-density lipoprotein levels and premature heart disease. This study aims to determine apolipoprotein B gene mutations among Malaysians with clinical diagnoses of familial hypercholesterolemia and to compare the phenotype of patients with apolipoprotein B gene mutations to those with a low-density lipoprotein receptor gene mutation. A group of 164 patients with a clinical diagnosis of familial hypercholesterolemia was analyzed. Amplicons in exon 26 and exon 29 of the apolipoprotein B gene were screened for genetic variants using denaturing gradient high-performance liquid chromatography; 10 variants were identified. Five novel mutations were detected (p.Gln2485Arg, p.Thr3526Ala, p.Glu3666Lys, p.Tyr4343CysfsX221, and p.Arg4297His). Those with familial defective apolipoprotein had a less severe phenotype than those with familial hypercholesterolemia. An apolipoprotein gene defect is present among Malaysian familial hypercholesterolemics. Those with both mutations show a more severe phenotype than those with one gene defect.

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.

Alternative splicing in the regulation of cholesterol homeostasis

PURPOSE OF REVIEW

With the advent of whole-transcriptome sequencing, or RNA-seq, we now know that alternative splicing is a generalized phenomenon, with nearly all multiexonic genes subject to alternative splicing. In this review, we highlight recent studies examining alternative splicing as a modulator of cellular cholesterol homeostasis and as an underlying mechanism of dyslipidemia.

RECENT FINDINGS

A number of key genes involved in cholesterol metabolism are known to undergo functionally relevant alternative splicing. Recently, we have identified coordinated changes in alternative splicing in multiple genes in response to alterations in cellular sterol content. We and others have implicated several splicing factors as regulators of lipid metabolism. Furthermore, a number of cis-acting human gene variants that modulate alternative splicing have been implicated in a variety of human metabolic diseases.

SUMMARY

Alternative splicing is of importance in various types of genetically influenced dyslipidemias and in the regulation of cellular cholesterol metabolism.

Low prevalence of mutations in known loci for autosomal dominant hypercholesterolemia in a multiethnic patient cohort

BACKGROUND- Autosomal dominant hypercholesterolemia (ADH), characterized by elevated plasma levels of low-density lipoprotein (LDL)-cholesterol, is caused by variants in at least 3 different genes: LDL receptor (LDLR), apolipoprotein B-100, and proprotein convertase subtilisin-like kexin type 9. There is paucity of data about the molecular basis of ADH among ethnic groups other than those of European or Japanese descent. Here, we examined the molecular basis of ADH in a multiethnic patient cohort from lipid clinics in a large, urban US city. METHODS AND RESULTS- A total of 38 men and 53 women, aged 22 to 76 years, met modified Simon-Broome criteria for ADH and were screened for mutations in the exons and consensus splice sites of LDLR, and in selected exons of apolipoprotein B-100 and proprotein convertase subtilisin-like kexin type 9. Deletions and duplications of LDLR exons were detected with multiplex ligation-dependent probe amplification. Heterozygous variants in LDLR were identified in 30 patients and in apolipoprotein B-100 in 1 patient. The remaining 60 patients (65%) had unexplained ADH. A higher proportion of blacks (77%) than either non-Hispanic whites (57%) or Hispanics (53%) had unexplained ADH. Compared with patients with LDLR variants, those with unexplained ADH had lower levels of LDL-cholesterol (292 ± 47 mg/dL versus 239 ± 42 mg/dL, respectively; P<0.0001) and higher levels of high-density lipoprotein cholesterol (45 ± 12 mg/dL versus 54 ± 13 mg/dL, respectively; P=0.003).

CONCLUSIONS

Our findings suggest that additional loci may contribute to ADH, especially in understudied populations such as blacks.