Polygenic influences on dyslipidemias

Tachol1 QTL on mouse chromosome 1 is responsible for hypercholesterolemia and diet-induced obesity

Hypercholesterolemia raises the risk for cardiovascular complications and overall health. Hypercholesterolemia is common, affecting 10% of the general population of the US, and heritable. Most individuals with hypercholesterolemia have a polygenic predisposition to the condition. Previously we identified a quantitative trait locus, Tachol1, linked to hypercholesterolemia on mouse chromosome 1 (Chr1) in a cross between C57BL/6J (B6) and TALLYHO/JngJ (TH) mice, a polygenic model for human obesity, type 2 diabetes and hyperlipidemia. Subsequently, using congenic mice that carry a TH-derived genomic segment of Chr1 on a B6 background, we demonstrated that the distal segment of Chr1, where Tachol1 maps, is necessary to cause hypercholesterolemia, as well as diet-induced obesity. In this study, we generated overlapping subcongenic lines to the distal segment of congenic region and characterized subcongenic mice carrying the smallest TH region of Tachol1, ~ 16.2 Mb in size (B6.TH-Chr1-16.2 Mb). Both male and female B6.TH-Chr1-16.2 Mb mice showed a significantly increased plasma total cholesterol levels compared to B6 on both chow and high fat (HF) diet. B6.TH-Chr1-16.2 Mb mice also had greater fat mass than B6 on HF diet, without increasing food intake. The gene and protein expression levels of absent in melanoma 2 (Aim2) gene were significantly upregulated in B6.TH-Chr1-16.2 Mb mice compared to B6. In summary, we confirmed the effect of Tachol1 on hypercholesterolemia and diet-induced obesity using subcongenic analysis.

LOX-1 in Cardiovascular Disease: A Comprehensive Molecular and Clinical Review

LOX-1, ORL-1, or lectin-like oxidized low-density lipoprotein receptor 1 is a transmembrane glycoprotein that binds and internalizes ox-LDL in foam cells. LOX-1 is the main receptor for oxidized low-density lipoproteins (ox-LDL). The LDL comes from food intake and circulates through the bloodstream. LOX-1 belongs to scavenger receptors (SR), which are associated with various cardiovascular diseases. The most important and severe of these is the formation of atherosclerotic plaques in the intimal layer of the endothelium. These plaques can evolve into complicated thrombi with the participation of fibroblasts, activated platelets, apoptotic muscle cells, and macrophages transformed into foam cells. This process causes changes in vascular endothelial homeostasis, leading to partial or total obstruction in the lumen of blood vessels. This obstruction can result in oxygen deprivation to the heart. Recently, LOX-1 has been involved in other pathologies, such as obesity and diabetes mellitus. However, the development of atherosclerosis has been the most relevant due to its relationship with cerebrovascular accidents and heart attacks. In this review, we will summarize findings related to the physiologic and pathophysiological processes of LOX-1 to support the detection, diagnosis, and prevention of those diseases.

Genetic variation in apolipoprotein A-V in hypertriglyceridemia

PURPOSE OF REVIEW

While biallelic rare APOA5 pathogenic loss-of-function (LOF) variants cause familial chylomicronemia syndrome, heterozygosity for such variants is associated with highly variable triglyceride phenotypes ranging from normal to severe hypertriglyceridemia, often in the same individual at different time points. Here we provide an updated overview of rare APOA5 variants in hypertriglyceridemia.

RECENT FINDINGS

Currently, most variants in APOA5 that are considered to be pathogenic according to guidelines of the American College of Medical Genetics and Genomics are those resulting in premature termination codons. There are minimal high quality functional data on the impact of most rare APOA5 missense variants; many are considered as variants of unknown or uncertain significance. Furthermore, particular common polymorphisms of APOA5 , such as p.Ser19Trp and p.Gly185Cys in Caucasian and Asian populations, respectively, are statistically overrepresented in hypertriglyceridemia cohorts and are sometimes misattributed as being causal for chylomicronemia, when they are merely risk alleles for hypertriglyceridemia.

SUMMARY

Both biallelic and monoallelic LOF variants in APOA5 are associated with severe hypertriglyceridemia, although the biochemical phenotype in the monoallelic state is highly variable and is often exacerbated by secondary factors. Currently, with few exceptions, the principal definitive mechanism for APOA5 pathogenicity is through premature truncation. The pathogenic mechanisms of most missense variants in APOA5 remain unclear and require additional functional experiments or family studies.

Polygenic risk for triglyceride levels in the presence of a high impact rare variant

BACKGROUND

Elevated triglyceride (TG) levels are a heritable and modifiable risk factor for cardiovascular disease and have well-established associations with common genetic variation captured in a polygenic risk score (PRS). In young adulthood, the 22q11.2 microdeletion conveys a 2-fold increased risk for mild-moderate hypertriglyceridemia. This study aimed to assess the role of the TG-PRS in individuals with this elevated baseline risk for mild-moderate hypertriglyceridemia.

METHODS

We studied a deeply phenotyped cohort of adults (n = 157, median age 34 years) with a 22q11.2 microdeletion and available genome sequencing, lipid level, and other clinical data. The association between a previously developed TG-PRS and TG levels was assessed using a multivariable regression model adjusting for effects of sex, BMI, and other covariates. We also constructed receiver operating characteristic (ROC) curves using logistic regression models to assess the ability of TG-PRS and significant clinical variables to predict mild-moderate hypertriglyceridemia status.

RESULTS

The TG-PRS was a significant predictor of TG-levels (p = 1.52E-04), along with male sex and BMI, in a multivariable model (pmodel = 7.26E-05). The effect of TG-PRS appeared to be slightly stronger in individuals with obesity (BMI ≥ 30) (beta = 0.4617) than without (beta = 0.1778), in a model unadjusted for other covariates (p-interaction = 0.045). Among ROC curves constructed, the inclusion of TG-PRS, sex, and BMI as predictor variables produced the greatest area under the curve (0.749) for classifying those with mild-moderate hypertriglyceridemia, achieving an optimal sensitivity and specificity of 0.746 and 0.707, respectively.

CONCLUSIONS

These results demonstrate that in addition to significant effects of sex and BMI, genome-wide common variation captured in a PRS also contributes to the variable expression of the 22q11.2 microdeletion with respect to elevated TG levels.

Variability of longitudinal triglyceride phenotype in patients heterozygous for pathogenic APOA5 variants

BACKGROUND

Biallelic pathogenic variants in APOA5 are an infrequent cause of familial chylomicronemia syndrome characterized by severe, refractory hypertriglyceridemia (HTG), and fasting plasma triglyceride (TG) >10 mmol/L (>875 mg/dL). The TG phenotype of heterozygous individuals with one copy of a pathogenic APOA5 variant is less familiar. We evaluated the longitudinal TG phenotype of individuals with a single pathogenic APOA5 variant allele.

METHODS

Medically stable outpatients from Ontario, Canada were selected for study based on having: 1) a rare pathogenic APOA5 variant in a single allele; and 2) at least three serial fasting TG measurements obtained over >1.5 years of follow-up.

RESULTS

Seven patients were followed for a mean of 5.3 ± 3.7 years. Fasting TG levels varied widely both within and between patients. Three patients displayed at least one normal TG measurement (<2.0 mmol/L or <175 mg/dL). All patients displayed mild-to-moderate HTG (2 to 9.9 mmol/L or 175 to 875 mg/dL) at multiple time points. Five patients displayed at least one severe HTG measurement. 10%, 54%, and 36% of all TG measurements were in normal, mild-to-moderate, and severe HTG ranges, respectively.

CONCLUSIONS

Heterozygosity for pathogenic variants in APOA5 is associated with highly variable TG phenotypes both within and between patients. Heterozygosity confers susceptibility to elevated TG levels, with secondary factors likely modulating the phenotypic severity.

Prevalence of lipoprotein lipase mutation in patients with severe hypertriglyceridemia and the characteristic features of hypertriglyceridemic pancreatitis

Aim: We conducted a retrospective study with the aim of determining the prevalence of lipoprotein lipase (LPL) mutation in patients with severe hypertriglyceridemia (HTG) and to study differences in characteristic features of HTG induced acute pancreatitis (AP). Materials and Methods: Seventy adults with a serum triglyceride (TG) level ≥500 mg/dL were included in the study. Baseline characteristics, LPL mutation and risk factors between those with and without HTG-AP were compared. Results: The mean age was 43 ± 12 years, and males accounted for 55.7%. Of the patients 35 had TG level

The advantages and pitfalls of genetic analysis in the diagnosis and management of lipid disorders

The increasing affordability of and access to next-generation DNA sequencing has increased the feasibility of incorporating genetic analysis into the diagnostic pathway for dyslipidaemia. But should genetic diagnosis be used routinely? DNA testing for any medical condition has potential benefits and pitfalls. For dyslipidaemias, the overall balance of advantages versus drawbacks differs according to the main lipid disturbance. For instance, some patients with severely elevated low-density lipoprotein cholesterol levels have a monogenic disorder, namely heterozygous familial hypercholesterolaemia. In these patients, DNA diagnosis can be definitive, in turn yielding several benefits for patient care that tend to outweigh any potential disadvantages. In contrast, hypertriglyceridaemia is almost always a polygenic condition without a discrete monogenic basis, except for ultrarare monogenic familial chylomicronaemia syndrome. Genetic testing in patients with hypertriglyceridaemia is therefore predominantly non-definitive and evidence for benefit is presently lacking. Here we consider advantages and limitations of genetic testing in dyslipidaemias.

Genetic testing in dyslipidaemia: An approach based on clinical experience

We have used DNA sequencing in our lipid clinic for >20 years. Dyslipidaemia is typically ascertained biochemically. For moderate deviations in the lipid profile, the etiology is often a combination of a polygenic susceptibility component plus secondary non-genetic factors. For severe dyslipidaemia, a monogenic etiology is more likely, although a discrete single-gene cause is frequently not found. A severe phenotype can also result from strong polygenic predisposition that is aggravated by secondary factors. A young age of onset plus a family history of dyslipidaemia or atherosclerotic cardiovascular disease can suggest a monogenic etiology. With severe dyslipidaemia, clinical examination focuses on detecting manifestations of monogenic syndromic conditions. For all patients with dyslipidaemia, secondary causes must be ruled out. Here we describe an experience-based practical approach to genetic testing of patients with severe deviations of low-density lipoprotein, triglycerides, high-density lipoprotein and also combined hyperlipidaemia and dysbetalipoproteinemia.

A new phenotypic classification system for dyslipidemias based on the standard lipid panel

Background

Dyslipoproteinemias can be classified by their distinct lipoprotein patterns, which helps determine atherosclerotic cardiovascular disease (ASCVD) risk and directs lipid management but this has required advanced laboratory testing.

Objective

To develop a new algorithm for classifying lipoprotein disorders that only relies on the standard lipid panel.

Methods

Lipid thresholds for defining the different lipoprotein phenotypes were derived for Non-High-Density Lipoprotein-Cholesterol (NonHDL-C) and Triglycerides (TG) to be concordant when possible with the current US Multi-Society guidelines for blood cholesterol management.

Results

The new classification method categorizes patients into all the classical Fredrickson-like phenotypes except for Type III dysbetalipoproteinemia. In addition, a new hypolipidemic phenotype (Type VI) due to genetic mutations in apoB-metabolism is described. The validity of the new algorithm was confirmed by lipid analysis by NMR (N = 11,365) and by concordance with classification by agarose gel electrophoresis/beta-quantification (N = 5504). Furthermore, based on the Atherosclerosis Risk in Communities (ARIC) cohort (N = 14,742), the lipoprotein phenotypes differ in their association with ASCVD (TypeV>IIb > IVb > IIa > IVa > normolipidemic) and can be used prognostically as risk enhancer conditions in the management of patients.

Conclusions

We describe a clinically useful lipoprotein phenotyping system that is only dependent upon the standard lipid panel. It, therefore, can be easily implemented for increasing compliance with current guidelines and for improving the care of patients at risk for ASCVD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01585-8.

A new algorithm is described for categorizing dyslipidemic patients into Fredrickson-like lipoprotein phenotypes except for Type III.

The new lipoprotein phenotypes were validated by NMR-lipoprotein analysis and by agarose gel electrophoresis/beta-quantification in a large number of subjects.

The new lipoprotein phenotyping system identifies high-risk cardiovascular patients and helps direct clinical management.

A major advance is that the new lipoprotein phenotypes are based on just the standard lipid panel, and thus can be automatically calculated by the clinical laboratory and widely implemented.

Beyond the Usual Suspects: Expanding on Mutations and Detection for Familial Hypercholesterolemia

Introduction: Familial hypercholesterolemia (FH) is a highly prevalent condition, predisposing individuals to premature cardiovascular disease and with a genetic basis more complex than initially thought. Advances in molecular technologies have provided novel insights into the role of next-generation-sequencing, the assessment and classification of newly found variants, the complex genotype-phenotype correlation, and the position of FH in the context of other dyslipidaemias.Areas covered: Understanding the scope of genetic determinants of FH has expanded substantially. This article reviews the current literature on the complexity that comes with this incremental knowledge and highlights the added value of genetic testing as an addition to phenotypic diagnosis of FH. Moreover, we discuss the broad genetic basis of FH, with a focus on the three main FH genes, but we also pay attention to polygenic hypercholesterolemia as well as minor and modulator genes involved in FH.Expert opinion: Both the availability and the need for genetic analysis of FH are on the rise as costs of sequencing continue to drop and new therapies require a genetic diagnosis for reimbursement. However, greater use of genetic testing requires more education of healthcare professionals, since molecular technologies will allow for rapid and accurate evaluation of large numbers of detected variants.

Translating genetic association of lipid levels for biological and clinical application

PURPOSE OF REVIEW

This review focuses on the foundational evidence from the last two decades of lipid genetics research and describes the current status of data-driven approaches for transethnic GWAS, fine-mapping, transcriptome informed fine-mapping, and disease prediction.

RECENT FINDINGS

Current lipid genetics research aims to understand the association mechanisms and clinical relevance of lipid loci as well as to capture population specific associations found in global ancestries. Recent genome-wide trans-ethnic association meta-analyses have identified 118 novel lipid loci reaching genome-wide significance. Gene-based burden tests of whole exome sequencing data have identified three genes-PCSK9, LDLR, and APOB-with significant rare variant burden associated with familial dyslipidemia. Transcriptome-wide association studies discovered five previously unreported lipid-associated loci. Additionally, the predictive power of genome-wide genetic risk scores amalgamating the polygenic determinants of lipid levels can potentially be used to increase the accuracy of coronary artery disease prediction.

CONCLUSIONS

Lipids are one of the most successful group of traits in the era of genome-wide genetic discovery for identification of novel loci and plausible drug targets. However, a substantial fraction of lipid trait heritability remains unexplained. Further analysis of diverse ancestries and state of the art methods for association locus refinement could potentially reveal some of this missing heritability and increase the clinical application of the genomic association results.

Machine learning modelling of blood lipid biomarkers in familial hypercholesterolaemia versus polygenic/environmental dyslipidaemia

Familial hypercholesterolaemia increases circulating LDL-C levels and leads to premature cardiovascular disease when undiagnosed or untreated. Current guidelines support genetic testing in patients complying with clinical diagnostic criteria and cascade screening of their family members. However, most of hyperlipidaemic subjects do not present pathogenic variants in the known disease genes, and most likely suffer from polygenic hypercholesterolaemia, which translates into a relatively low yield of genetic screening programs. This study aims to identify new biomarkers and develop new approaches to improve the identification of individuals carrying monogenic causative variants. Using a machine-learning approach in a paediatric dataset of individuals, tested for disease causative genes and with an extended lipid profile, we developed new models able to classify familial hypercholesterolaemia patients with a much higher specificity than currently used methods. The best performing models incorporated parameters absent from the most common FH clinical criteria, namely apoB/apoA-I, TG/apoB and LDL1. These parameters were found to contribute to an improved identification of monogenic individuals. Furthermore, models using only TC and LDL-C levels presented a higher specificity of classification when compared to simple cut-offs. Our results can be applied towards the improvement of the yield of genetic screening programs and corresponding costs.

Do we measure or compute polygenic risk scores? Why language matters

Here, we argue that polygenic risk scores (PRSs) are different epistemic objects as compared to other biomarkers such as blood pressure or sodium level. While the latter two may be subject to variation, measured inaccurately or interpreted in various ways, blood flow has pressure and sodium is available in a concentration that can be quantified and visualised. In stark contrast, PRSs are calculated, compiled or constructed through the statistical assemblage of genetic variants. How researchers frame and name PRSs has consequences for how we interpret and value their results. We distinguish between the tangible and inferential understanding of PRS and the corresponding languages of measurement and computation, respectively. The conflation of these frames obscures important questions we need to ask: what PRS seeks to represent, whether current ways of 'doing PRS' are optimal and responsible, and upon what we base the credibility of PRS-based knowledge claims.

Ancestry-specific profiles of genetic determinants of severe hypertriglyceridemia

BACKGROUND

Susceptibility to severe hypertriglyceridemia (HTG), defined as plasma triglyceride (TG) levels ≥10 mmol/L (880 mg/dL), is conferred by both heterozygous rare variants in five genes involved in TG metabolism and numerous common single-nucleotide polymorphisms (SNPs) associated with TG levels.

OBJECTIVE

To date, these genetic susceptibility factors have been comprehensively assessed primarily in severe HTG patients of European ancestry. Here, we expand our analysis to HTG patients of East Asian and Hispanic ancestry.

METHODS

The genomic DNA of 336, 63 and 199 severe HTG patients of European, East Asian and Hispanic ancestry, respectively, was evaluated using a targeted next-generation sequencing panel to screen for: 1) rare variants in LPL, APOA5, APOC2, GPIHBP1 and LMF1; 2) common, small-to-moderate effect SNPs, quantified using a polygenic score; and 3) common, large-effect polymorphisms, APOA5 p.G185C and p.S19W.

RESULTS

While the proportion of individuals with high polygenic scores was similar, frequency of rare variant carriers varied across ancestries. Compared with ancestry-matched controls, Hispanic patients were the most likely to have a rare variant (OR = 5.02; 95% CI 3.07-8.21; p < 0.001), while European patients were the least likely (OR = 2.56; 95% CI 1.58-4.13; p < 0.001). The APOA5 p.G185C polymorphism, exclusive to East Asians, was significantly enriched in patients compared with controls (OR = 10.1; 95% CI 5.6-18.3; p < 0.001), showing the highest enrichment among the measured genetic factors.

CONCLUSION

While TG-associated rare variants and common SNPs are both found in statistical excess in severe HTG patients of different ancestral backgrounds, the overall genetic profiles of each ancestry group were distinct.

Genome-scale CRISPR screening for modifiers of cellular LDL uptake

Hypercholesterolemia is a causal and modifiable risk factor for atherosclerotic cardiovascular disease. A critical pathway regulating cholesterol homeostasis involves the receptor-mediated endocytosis of low-density lipoproteins into hepatocytes, mediated by the LDL receptor. We applied genome-scale CRISPR screening to query the genetic determinants of cellular LDL uptake in HuH7 cells cultured under either lipoprotein-rich or lipoprotein-starved conditions. Candidate LDL uptake regulators were validated through the synthesis and secondary screening of a customized library of gRNA at greater depth of coverage. This secondary screen yielded significantly improved performance relative to the primary genome-wide screen, with better discrimination of internal positive controls, no identification of negative controls, and improved concordance between screen hits at both the gene and gRNA level. We then applied our customized gRNA library to orthogonal screens that tested for the specificity of each candidate regulator for LDL versus transferrin endocytosis, the presence or absence of genetic epistasis with LDLR deletion, the impact of each perturbation on LDLR expression and trafficking, and the generalizability of LDL uptake modifiers across multiple cell types. These findings identified several previously unrecognized genes with putative roles in LDL uptake and suggest mechanisms for their functional interaction with LDLR.

Combined hyperlipidemia is genetically similar to isolated hypertriglyceridemia

BACKGROUND

Combined hyperlipidemia (CHL) is a common disorder defined by concurrently elevated low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels. Despite decades of study, the genetic basis of CHL remains unclear.

OBJECTIVE

To characterize the genetic profiles of patients with CHL and compare them to those in patients with isolated hypercholesterolemia and isolated hypertriglyceridemia (HTG).

METHODS

DNA from 259, 379 and 124 patients with CHL, isolated hypercholesterolemia and isolated HTG, respectively, underwent targeted sequencing. We assessed: 1) rare variants disrupting canonical LDL-C or TG metabolism genes; and 2) two polygenic scores-for elevated LDL-C and TG-calculated using common trait-associated single-nucleotide polymorphisms (SNPs). Genetic profiles were compared against 1000 Genomes Project controls.

RESULTS

Both CHL and isolated HTG patients had significantly increased odds of a high polygenic score for TG: 2.50 (95% confidence interval [CI] 1.61-3.88; P < 0.001) and 3.72 (95% CI 2.24-6.19; P < 0.001), respectively. CHL patients had neither a significant accumulation of rare variants for LDL-C or TG, nor a high polygenic score for LDL-C. In contrast, patients with isolated hypercholesterolemia had a 3.03-fold increased odds (95% CI 2.22-4.13; P < 0.001) of carrying rare variants associated with familial hypercholesterolemia, while patients with isolated HTG had a 2.78-fold increased odds (95% CI 1.27-6.10; P = 0.0136) of carrying rare variants associated with severe HTG.

CONCLUSION

CHL is genetically similar to isolated HTG, a known polygenic trait. Both cohorts had a significant accumulation of common TG-raising variants. Elevated LDL-C levels in CHL are not associated with common or rare LDL-C-related genetic variants.

Phenotypic Differences Between Polygenic and Monogenic Hypobetalipoproteinemia

OBJECTIVE

Primary hypobetalipoproteinemia is characterized by LDL-C (low-density lipoprotein cholesterol) concentrations below the fifth percentile. Primary hypobetalipoproteinemia mostly results from heterozygous mutations in the APOB (apolipoprotein B) and PCSK9 genes, and a polygenic origin is hypothesized in the remaining cases. Hypobetalipoproteinemia patients present an increased risk of nonalcoholic fatty liver disease and steatohepatitis. Here, we compared hepatic alterations between monogenic, polygenic, and primary hypobetalipoproteinemia of unknown cause. Approach and Results: Targeted next-generation sequencing was performed in a cohort of 111 patients with hypobetalipoproteinemia to assess monogenic and polygenic origins using an LDL-C-dedicated polygenic risk score. Forty patients (36%) had monogenic hypobetalipoproteinemia, 38 (34%) had polygenic hypobetalipoproteinemia, and 33 subjects (30%) had hypobetalipoproteinemia from an unknown cause. Patients with monogenic hypobetalipoproteinemia had lower LDL-C and apolipoprotein B plasma levels compared with those with polygenic hypobetalipoproteinemia. Liver function was assessed by hepatic ultrasonography and liver enzymes levels. Fifty-nine percent of patients with primary hypobetalipoproteinemia presented with liver steatosis, whereas 21% had increased alanine aminotransferase suggestive of liver injury. Monogenic hypobetalipoproteinemia was also associated with an increased prevalence of liver steatosis (81% versus 29%, P<0.001) and liver injury (47% versus 0%) compared with polygenic hypobetalipoproteinemia.

CONCLUSIONS

This study highlights the importance of genetic diagnosis in the clinical care of primary hypobetalipoproteinemia patients. It shows for the first time that a polygenic origin of hypobetalipoproteinemia is associated with a lower risk of liver steatosis and liver injury versus monogenic hypobetalipoproteinemia. Thus, polygenic risk score is a useful tool to establish a more personalized follow-up of primary hypobetalipoproteinemia patients.

High-Sensitivity C-Reactive Protein and Carotid Intima Media Thickness as Markers of Subclinical Inflammation and Atherosclerosis in Pediatric Patients with Hypercholesterolemia

Hypercholesterolemia is a major cause of atherosclerosis development and premature cardiovascular disease (CVD). It leads to inflammation, which further accelerates atherosclerosis progression. Familial hypercholesterolemia (FH) is an autosomal dominant disorder characterized by elevated serum LDL-c from birth, due to a disease-causing variant in one of the causative genes (LDLR, APOB, PCSK9). In polygenic hypercholesterolemia (PH), the disease-causing genetic variant is absent; it is likely the cumulative result of multiple single nucleotide polymorphisms in LDL metabolism-related genes and other factors, such as lifestyle and environment. In high risk groups, such as patients with FH, an effective primary prevention of CVD must begin in childhood. High-sensitivity C-reactive protein (hsCRP) and carotid intima media thickness (cIMT) are two potential minimally invasive correlates of inflammation and subclinical atherosclerosis progression. hsCRP and cIMT have been shown to be significantly increased in patients with FH and PH relative to healthy controls, with some studies yielding conflicting results. In this review, we aim to summarize current knowledge and recent findings regarding the applicability of hsCRP and cIMT as markers of low-grade inflammation and subclinical atherosclerosis, focusing especially on children and adolescents with hypercholesterolemia.

Development of a new expanded next-generation sequencing panel for genetic diseases involved in dyslipidemia

The aim of this study was to provide an efficient tool: reliable, able to increase the molecular diagnosis performance, to facilitate the detection of copy number variants (CNV), to assess genetic risk scores (wGRS) and to offer the opportunity to explore candidate genes. Custom SeqCap EZ libraries, NextSeq500 sequencing and a homemade pipeline enable the analysis of 311 dyslipidemia-related genes. In the training group (48 DNA from patients with a well-established molecular diagnosis), this next-generation sequencing (NGS) workflow showed an analytical sensitivity >99% (n = 532 variants) without any false negative including a partial deletion of one exon. In the prospective group, from 25 DNA from patients without prior molecular analyses, 18 rare variants were identified in the first intention panel genes, allowing the diagnosis of monogenic dyslipidemia in 11 patients. In six other patients, the analysis of minor genes and wGRS determination provided a hypothesis to explain the dyslipidemia. Remaining data from the whole NGS workflow identified four patients with potentially deleterious variants. This NGS process gives a major opportunity to accede to an enhanced understanding of the genetic of dyslipidemia by simultaneous assessment of multiple genetic determinants.

2019 George Lyman Duff Memorial Lecture: Three Decades of Examining DNA in Patients With Dyslipidemia

Dyslipidemias include both rare single gene disorders and common conditions that have a complex underlying basis. In London, ON, there is fortuitous close physical proximity between the Lipid Genetics Clinic and the London Regional Genomics Centre. For >30 years, we have applied DNA sequencing of clinical samples to help answer scientific questions. More than 2000 patients referred with dyslipidemias have participated in an ongoing translational research program. In 2013, we transitioned to next-generation sequencing; our targeted panel is designed to concurrently assess both monogenic and polygenic contributions to dyslipidemias. Patient DNA is screened for rare variants underlying 25 mendelian dyslipidemias, including familial hypercholesterolemia, hepatic lipase deficiency, abetalipoproteinemia, and familial chylomicronemia syndrome. Furthermore, polygenic scores for LDL (low-density lipoprotein) and HDL (high-density lipoprotein) cholesterol, and triglycerides are calculated for each patient. We thus simultaneously document both rare and common genetic variants, allowing for a broad view of genetic predisposition for both individual patients and cohorts. For instance, among patients referred with severe hypertriglyceridemia, defined as ≥10 mmol/L (≥885 mg/dL), <1% have a mendelian disorder (ie, autosomal recessive familial chylomicronemia syndrome), ≈15% have heterozygous rare variants (a >3-fold increase over normolipidemic individuals), and ≈35% have an extreme polygenic score (a >3-fold increase over normolipidemic individuals). Other dyslipidemias show a different mix of genetic determinants. Genetic results are discussed with patients and can support clinical decision-making. Integrating DNA testing into clinical care allows for a bidirectional flow of information, which facilitates scientific discoveries and clinical translation.

Failure of cosegregation between a rare STAP1 missense variant and hypercholesterolemia

Autosomal dominant familial hypercholesterolemia (FH) is characterized by elevated low-density lipoprotein cholesterol levels and an increased risk for atherosclerotic cardiovascular disease. Although rare pathogenic variants in genes encoding the low-density lipoprotein receptor, apolipoprotein B, proprotein convertase subtilisin/kexin 9 are found in more than 80% of molecularly defined patients with FH, a few rare minor causative genes have been proposed, including the gene encoding signal-transducing adaptor family member 1 (STAP1). Here, we describe a patient with hypercholesterolemia and the rare heterozygous missense variant p.D207N in STAP1. However, extending the pedigree showed failure of the variant to cosegregate with hypercholesterolemia, as both his sons were carriers of the variant and both were also normolipidemic. The findings add to the evidence against STAP1 as a genetic locus for FH.

Can genetic testing help in the management of dyslipidaemias?

PURPOSE OF REVIEW

The aim of this study was to evaluate the potential role of genetic testing, particularly next-generation DNA sequencing, in diagnosing and managing dyslipidaemias, particularly monogenic dyslipidaemias.

RECENT FINDINGS

Targeted DNA sequencing of the genes causing monogenic dyslipidaemias is becoming more accessible. Some societies' position statements advise selective utilization of DNA testing in combination with clinical and biochemical assessment. However, high-quality peer-reviewed evidence showing that a DNA-based diagnosis impacts upon long-term patient outcomes is currently lacking. Nonetheless, we show anecdotal examples of tangible clinical actions following from a genetic diagnosis. In any event, care must be taken when interpreting genetic reports. We strongly feel that expertise in both genetics and dyslipidaemias is required to adequately interpret and report results to patients, as well as to make informed treatment decisions that can have a potential lifelong impact.

SUMMARY

There are some examples of monogenic dyslipidaemias for which having a molecular diagnosis might beneficially affect patient outcomes, for example certain cases of suspected familial hypercholesterolemia, familial chylomicronemia syndrome, sitosterolemia or lysosomal acid lipase deficiency. In general, we recommend limiting genetic testing to selected cases of monogenic dyslipidaemias. Finally, we advise that there is currently no proven clinical benefit in testing for polygenic dyslipidaemias.

Pediatric Dyslipidemia-Beyond Familial Hypercholesterolemia

Dyslipidemia is seen with increasing prevalence in young Canadians, mainly mild to moderate hypertriglyceridemia secondary to obesity. This review focuses on pediatric dyslipidemias excluding familial hypercholesterolemia (FH), but including both severe and mild to moderate hypertriglyceridemia, combined hyperlipidemia, and elevated lipoprotein(a) [Lp(a)]. We suggest that for Canadian children and adolescents with dyslipidemia, atherosclerotic cardiovascular disease (ASCVD) risk assessment should include both low-density lipoprotein cholesterol and triglyceride measurement. To further stratify risk, determination of non-high-density lipoprotein cholesterol is recommended, for both its ability to predict ASCVD and convenience for the patient because fasting is not required. Similarly, apolipoprotein B measurement (fasting or nonfasting), where available, can be helpful. Lp(a) measurement should not be routine in childhood, but it can be considered in special circumstances. After ruling out secondary causes, the foundation for management of pediatric dyslipidemia includes weight regulation, optimizing diet, and increasing activity level. At present, randomized clinical trial data to guide pharmaceutical management of pediatric hypertriglyceridemia or other non-FH pediatric dyslipidemias are scarce. Pharmaceutical management should be reserved for special situations in which risk of complications such as acute pancreatitis or ASCVD over the intermediate term is high and conservative lifestyle-based interventions have been ineffective.

Apolipoprotein C-II: the re-emergence of a forgotten factor

PURPOSE OF REVIEW

Apolipoprotein C-II (apoC-II) is a critical cofactor for the activation of lipoprotein lipase (LPL), a plasma enzyme that hydrolyzes triglycerides (TG) on TG-rich lipoproteins (TRL). Although apoC-II was first discovered nearly 50 years ago, there is renewed interest in it because of the recent efforts to develop new drugs for the treatment of hypertriglyceridemia (HTG). The main topic of this review will be the development of apoC-II mimetic peptides as a possible new therapy for cardiovascular disease.

RECENT FINDINGS

We first describe the biochemistry of apoC-II and its role in TRL metabolism. We then review the clinical findings of HTG, particularly those related to apoC-II deficiency, and how TG metabolism relates to the development of atherosclerosis. We next summarize the current efforts to develop new drugs for HTG. Finally, we describe recent efforts to make small synthetic apoC-II mimetic peptides for activation of LPL and how these peptides unexpectedly have other mechanisms of action mostly related to the antagonism of the TG-raising effects of apoC-III.

SUMMARY

The role of apoC-II in TG metabolism is reviewed, as well as recent efforts to develop apoC-II mimetic peptides into a novel therapy for HTG.

A polygenic biomarker to identify patients with severe hypercholesterolemia of polygenic origin

Background

Severe hypercholesterolemia (HC, LDL‐C > 4.9 mmol/L) affects over 30 million people worldwide. In this study, we validated a new polygenic risk score (PRS) for LDL‐C.

Methods

Summary statistics from the Global Lipid Genome Consortium and genotype data from two large populations were used.

Results

A 36‐SNP PRS was generated using data for 2,197 white Americans. In a replication cohort of 4,787 Finns, the PRS was strongly associated with the LDL‐C trait and explained 8% of its variability (p = 10^–41). After risk categorization, the risk of having HC was higher in the high‐ versus low‐risk group (RR = 4.17, p < 1 × 10⁻⁷). Compared to a 12‐SNP LDL‐C raising score (currently used in the United Kingdom), the PRS explained more LDL‐C variability (8% vs. 6%). Among Finns with severe HC, 53% (66/124) versus 44% (55/124) were classified as high risk by the PRS and LDL‐C raising score, respectively. Moreover, 54% of individuals with severe HC defined as low risk by the LDL‐C raising score were reclassified to intermediate or high risk by the new PRS.

Conclusion

The new PRS has a better predictive role in identifying HC of polygenic origin compared to the currently available method and can better stratify patients into diagnostic and therapeutic algorithms.

Severe Combined Dyslipidemia With a Complex Genetic Basis

Background. Familial dysbetalipoproteinemia (also known as type 3 hyperlipoproteinemia) is typically associated with homozygosity for the apolipoprotein E2 isoform, but also sometimes with dominant rare missense variants in the APOE gene. Patients present with roughly equimolar elevations of cholesterol and triglyceride (TG) due to pathologic accumulation of remnant lipoprotein particles. Clinical features include tuberoeruptive xanthomas, palmar xanthomas, and premature vascular disease. Case. A 48-year-old male presented with severe combined dyslipidemia: total cholesterol and TG were 11.5 and 21.4 mmol/L, respectively. He had dyslipidemia since his early 20s, with tuberous xanthomas on his elbows and knees. His body mass index was 42 kg/m². He also had treated hypertension, mild renal impairment, and a history of gout. He had no history of cardiovascular disease, peripheral arterial disease, or pancreatitis. Multiple medications had been advised including rosuvastatin, ezetimibe, fenofibrate, and alirocumab, but his lipid levels were never adequately controlled. Genetic Analysis. Targeted next-generation sequencing identified (1) the APOE E2/E2 homozygous genotype classically described with familial dysbetalipoproteinemia; (2) in addition, one APOE E2 allele contained the rare heterozygous missense variant p.G145D, previously termed apo E-Bethesda; (3) a rare heterozygous APOC2 nonsense variant p.Q92X; and (4) a high polygenic risk score for TG levels (16 out of 28 TG-raising alleles) at the 82nd percentile for age and sex. Conclusion. The multiple genetic "hits" on top of the classical APOE E2/E2 genotype likely explain the more severe dyslipidemia and refractory clinical phenotype.

Genetic risk scores in lipid disorders

PURPOSE OF REVIEW

Extensive work has gone into understanding the genetics of cardiovascular disease (CVD) and implicating genes involved in hyperlipidaemia. Translation into routine practise involves using genetic risk scores (GRS) to identify high-risk individuals in the general population. Some of these risk scores are beginning to disentangle the complex nature of CVD and inherited dyslipidaemias.

RECENT FINDINGS

GRS of varying complexity have been used to identify high-risk groups of patients with polygenic CVD including some individuals with risk equivalent to monogenic disease. In phenotypic familial hypercholesterolaemia a six or 12 gene lipid GRS may identify polygenic cases that comprise up to 50% of cases. In high triglyceride syndromes including even cases of familial chylomicronaemia syndrome more than 80% of cases are polygenic and not even associated with rare variants. In both familial hypercholesterolaemia and familial chylomicronaemia syndrome individuals with polygenic disease have a lower risk than those with monogenic disease.

SUMMARY

GRS show promise in identifying individuals with high risks of CVD. They have a close relationship with imaging markers. It is unclear whether GRS, imaging or both will be used to identify individuals at high risk of future events.

Six years' experience with LipidSeq: clinical and research learnings from a hybrid, targeted sequencing panel for dyslipidemias

BACKGROUND

In 2013, our laboratory designed a targeted sequencing panel, "LipidSeq", to study the genetic determinants of dyslipidemia and metabolic disorders. Over the last 6 years, we have analyzed 3262 patient samples obtained from our own Lipid Genetics Clinic and international colleagues. Here, we highlight our findings and discuss research benefits and clinical implications of our panel.

METHODS

LipidSeq targets 69 genes and 185 single-nucleotide polymorphisms (SNPs) either causally related or associated with dyslipidemia and metabolic disorders. This design allows us to simultaneously evaluate monogenic-caused by rare single-nucleotide variants (SNVs) or copy-number variants (CNVs)-and polygenic forms of dyslipidemia. Polygenic determinants were assessed using three polygenic scores, one each for low-density lipoprotein cholesterol, triglyceride, and high-density lipoprotein cholesterol.

RESULTS

Among 3262 patient samples evaluated, the majority had hypertriglyceridemia (40.1%) and familial hypercholesterolemia (28.3%). Across all samples, we identified 24,931 unique SNVs, including 2205 rare variants predicted disruptive to protein function, and 77 unique CNVs. Considering our own 1466 clinic patients, LipidSeq results have helped in diagnosis and improving treatment options.

CONCLUSIONS

Our LipidSeq design based on ontology of lipid disorders has enabled robust detection of variants underlying monogenic and polygenic dyslipidemias. In more than 50 publications related to LipidSeq, we have described novel variants, the polygenic nature of many dyslipidemias-some previously thought to be primarily monogenic-and have uncovered novel mechanisms of disease. We further demonstrate several tangible clinical benefits of its use.

The polygenic nature of mild-to-moderate hypertriglyceridemia

BACKGROUND

Patients with mild-to-moderate hypertriglyceridemia (HTG) are thought to share specific genetic susceptibility factors that are also present in patients with severe HTG, but no data have been reported on this issue.

OBJECTIVE

The objective of this study was to characterize genetic profiles of patients with mild-to-moderate HTG and compare them to patients with severe HTG.

METHODS

DNA from patients with mild-to-moderate HTG was sequenced using our targeted sequencing panel, "LipidSeq". For each patient, we assessed 1) rare variants disrupting five TG metabolism genes and 2) the accumulation of 16 common single-nucleotide polymorphisms (SNPs) using a polygenic risk score. The genetic profiles for these patients were then compared with normolipidemic controls from the 1000 Genomes Project and with patients with severe HTG.

RESULTS

Across 134 patients with mild-to-moderate HTG, 9.0% carried heterozygous rare variants and 26.9% had an excess accumulation of common SNPs. Patients with mild-to-moderate HTG were 2.38 times (95% CI [1.13-4.99]; P = .021) more likely to carry a rare variant and 3.26 times (95% CI [2.02-5.26]; P < .0001) more likely to have an extreme polygenic risk score compared with the 1000 Genomes Project. In addition, patients with severe HTG were 1.86 times (95% CI [0.98-3.51]; P = .032) more likely to carry a rare variant and 1.63 times (95% CI [1.07-2.48]; P = .013) more likely to have an extreme polygenic risk score than patients with mild-to-moderate HTG.

CONCLUSIONS

We report an increased prevalence of genetic determinants in patients with an increased severity of the HTG phenotype when considering either rare variants disrupting TG metabolism genes or an excess accumulation of common SNPs. As well, the findings confirm that the most prevalent genetic contributor to HTG, regardless of severity, is polygenic SNP accumulation.

Genetics of Hypertriglyceridemia

Hypertriglyceridemia, a commonly encountered phenotype in cardiovascular and metabolic clinics, is surprisingly complex. A range of genetic variants, from single-nucleotide variants to large-scale copy number variants, can lead to either the severe or mild-to-moderate forms of the disease. At the genetic level, severely elevated triglyceride levels resulting from familial chylomicronemia syndrome (FCS) are caused by homozygous or biallelic loss-of-function variants in LPL, APOC2, APOA5, LMF1, and GPIHBP1 genes. In contrast, susceptibility to multifactorial chylomicronemia (MCM), which has an estimated prevalence of ~1 in 600 and is at least 50-100-times more common than FCS, results from two different types of genetic variants: (1) rare heterozygous variants (minor allele frequency <1%) with variable penetrance in the five causal genes for FCS; and (2) common variants (minor allele frequency >5%) whose individually small phenotypic effects are quantified using a polygenic score. There is indirect evidence of similar complex genetic predisposition in other clinical phenotypes that have a component of hypertriglyceridemia, such as combined hyperlipidemia and dysbetalipoproteinemia. Future considerations include: (1) evaluation of whether the specific type of genetic predisposition to hypertriglyceridemia affects medical decisions or long-term outcomes; and (2) searching for other genetic contributors, including the role of genome-wide polygenic scores, novel genes, non-linear gene-gene or gene-environment interactions, and non-genomic mechanisms including epigenetics and mitochondrial DNA.

Rare dyslipidaemias, from phenotype to genotype to management: a European Atherosclerosis Society task force consensus statement

Genome sequencing and gene-based therapies appear poised to advance the management of rare lipoprotein disorders and associated dyslipidaemias. However, in practice, underdiagnosis and undertreatment of these disorders are common, in large part due to interindividual variability in the genetic causes and phenotypic presentation of these conditions. To address these challenges, the European Atherosclerosis Society formed a task force to provide practical clinical guidance focusing on patients with extreme concentrations (either low or high) of plasma low-density lipoprotein cholesterol, triglycerides, or high-density lipoprotein cholesterol. The task force also recognises the scarcity of quality information regarding the prevalence and outcomes of these conditions. Collaborative registries are needed to improve health policy for the care of patients with rare dyslipidaemias.

Conservative management in hypertriglyceridemia-associated pancreatitis

BACKGROUND

Severe hypertriglyceridemia (serum triglyceride >10 mmol L^-1 ) is implicated in ~9% of acute pancreatitis cases. Certain guidelines list severe hypertriglyceridemia as an indication for plasmapheresis.

OBJECTIVE

We assembled the natural trajectory of triglyceride levels in patients with acute pancreatitis due to severe hypertriglyceridemia who were managed conservatively without plasmapheresis to evaluate the effectiveness of this approach.

METHODS

A retrospective chart review was performed on 22 hospital admissions for acute pancreatitis episodes considered to be caused by severe hypertriglyceridemia. Patients were managed supportively, with cessation of oral intake (NPO) and intravenous hydration. Insulin infusion was used in 12 patients to manage concurrent hyperglycaemia.

RESULTS

Triglyceride levels for the group were evaluated using a mixed-effects model. The average triglyceride level fell from 45.4 mmol L^-1 on presentation to 13.3 mmol L^-1 within 48 h, corresponding to a mean 69.8% decrease. Regression analysis showed a triglyceride half-life of 30.6 h. Findings were similar for NPO-only and insulin infusion subgroups.

CONCLUSION

Patients with severe hypertriglyceridemia and acute pancreatitis can be conservatively managed safely and effectively without plasmapheresis.

Identification of a novel LDLR disease-causing variant using capture-based next-generation sequencing screening of familial hypercholesterolemia patients in Taiwan

BACKGROUND AND AIMS

Familial hypercholesterolemia (FH) is an autosomal dominant disorder with paramount health impacts. However, less than 1% FH patients in Taiwan were formally diagnosed, partly due to the lack of reliable cost-effective genetic testing. We aimed at using a next-generation sequencing (NGS) platform as the clinical genetic testing method for FH.

METHODS

We designed probes to capture the whole LDLR gene and all coding sequences of APOB and PCSK9, and then sequenced with Illumina MiSeq platform (2 × 300 bps). The entire pipeline was tested on 13 DNA samples with known causative variants (including 3 large duplications and 2 large deletions). Then we enrolled a new cohort of 28 unrelated FH patients with Dutch Lipid Clinic Network score ≥5. Relatives were included in the cascade screening.

RESULTS

From the 13 DNA samples, we correctly identify all the variants, including big duplications and deletions. From the new cohort, we identified the causative variants in 21 of the 28 unrelated probands; five of them carrying a novel splice site variant c.1186+2T>G in LDLR. Among the family members, the concentration of LDL cholesterol was 7.82 ± 2.13 mmol/l in LDLR c.1186+2T>G carrier group (n = 26), and was significantly higher than 3.18 ± 1.36 mmol/l in the non-carrier group (n = 25).

CONCLUSIONS

This is the first capture-based NGS testing for FH to cover the whole LDLR genomic region, and therefore making reliable structural variation detection. This panel can comprehensively detect disease-causing variants in LDLR, APOB, and PCSK9 for FH patients.

Current pharmacotherapy for the treatment of dyslipidemia associated with HIV infection

Introduction: Cardiovascular disease is an important cause of morbidity and mortality in persons with human immunodeficiency virus (PWH). The risk of atherosclerotic cardiovascular disease (ASCVD) is higher in PWH compared to uninfected persons. Dyslipidemia is a critical link in the pathogenesis of ASCVD in PWH. Chronic inflammation associated with HIV infection may drive both dyslipidemia and ASCVD. Areas covered: The authors review the evidence for using lipid-lowering therapy in PWH and includes an overview of the utility and complexity of using statins in PWH, in particular, drug interactions, safety, and efficacy. In addition, data covering alternate therapies like omega-3 fatty acids, fibrates, niacin, ezetimibe, and PCSK-9 inhibitors are reviewed. Expert opinion: Dyslipidemia is a common problem in PWH. The risk of ASCVD is higher in PWH. Lipid-lowering therapy reduces the risk of ASCVD, but clinical endpoint trials are lacking in PWH. Statin therapy is the mainstay of primary prevention for ASCVD. The timing of when to initiate primary prevention with statins in PWH is unclear. Beyond statins, there are limited data that other lipid-lowering agents have utility in PWH. Ongoing trials like the REPRIEVE trial will inform the community about the optimal approach to lipid-lowering therapy in PWH.

Genetic Determinants of Myocardial Infarction Risk in Familial Hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is an inherited condition of elevated serum low-density lipoprotein (LDL) cholesterol leading to premature coronary heart disease. We evaluated whether FH mutations are independently associated with the development of myocardial infarction (MI), after adjusting for LDL cholesterol level and clinical risk factors.

METHODS

In 182 unrelated patients from different families referred with clinically suspected FH, targeted next-generation DNA sequencing was performed on 73 lipid-related genes and 178 single nucleotide polymorphisms, at 300-times mean read depth, to identify monogenic mutations and high-risk single nucleotide polymorphisms.

RESULTS

Pathogenic FH mutations were identified in 27% of patients. Patients with mutations, compared with those without, were 12 years younger when referred to the lipid clinic (P < 0.001) and had higher baseline and post-treatment LDL cholesterol by 1.11 mmol/L (P < 0.001) and 0.62 mmol/L (P = 0.01), respectively. The hazard ratio for premature MI with respect to having an FH mutation, controlling for sex, hypertension, body mass index, diabetes, LDL cholesterol, and smoking, was 4.51 (P = 0.002).

CONCLUSION

FH is a genetically diverse condition. FH mutations are independently associated with higher risk of premature MI in patients referred for hypercholesterolemia. Therefore, genotyping could guide cardiovascular risk stratification in the personalized treatment of FH.

The evolution of genetic-based risk scores for lipids and cardiovascular disease

PURPOSE OF REVIEW

With improved next-generation sequencing technology, open-access genetic databases and increased awareness of complex trait genetics, we are entering a new era of risk assessment in which genetic-based risk scores (GRSs) will play a clinical role. We review the concepts underlying polygenic models of disease susceptibility and challenges in clinical implementation.

RECENT FINDINGS

Polygenic risk scores are currently used in genetic research on dyslipidemias and cardiovascular disease (CVD). Although the underlying principles for constructing polygenic scores for lipids are established, the lack of consensus on which score to use is indicated by the large number - about 50 - that have been published. Recently, large-scale polygenic scores for CVD appear to afford superior risk prediction compared to small-scale scores. Despite the potential benefits of GRSs, certain biases towards ethnicity and sex need to be worked through.

SUMMARY

We are on the verge of clinical application of GRSs to provide incremental information on dyslipidemia and CVD risk above and beyond traditional clinical variables. Additional work is required to develop a consensus of how such scores will be constructed and measured in a validated manner, as well as clinical indications for their use.

The biochemical and genetic diagnosis of lipid disorders

PURPOSE OF REVIEW

To examine recent advances in our knowledge on the diagnosis of lipid disorders.

RECENT FINDINGS

Fasting values above the 99th percentile for direct LDL-cholesterol (LDL-C), lipoprotein(a), and triglycerides are greater than 225 mg/dl, greater than 160 mg/dl, and greater than 500 mg/dl (>5.82, >394, and >5.65 mmol/l), respectively, whereas such values for plasma lathosterol, β-sitosterol, and cholestanol are greater than 8.0, 8.0, and 5.0 mg/l (>0.021, 0.019, and 0.013 mmol/l), respectively. Values below the first percentile for LDL-C are less than 40 mg/dl (<1.03 mmol/l) and for HDL-cholesterol (HDL-C) less than 25 mg/dl (<0.65 mmol/l) in men and less than 30 mg/dl (<0.78 mmol/l) in women, respectively. The above values can predispose to premature CVD, pancreatitis, neurologic disease, and kidney failure, and may be associated with monogenic lipid disorders. In the absence of secondary causes including diabetes or kidney, liver, or thyroid disease, consideration should be given to sequencing the following genes: ABCA1, ABCG5, ABCG8, APOA1, APOA5, APOB, APOC2, APOE, CETP, CYP27A1, GPIHBP1, LCAT, LDLR, LDLRAP1, LIPA, LIPC, LMF1, LPL, MTTP, PCSK9, SCARB1, and STAP1.

SUMMARY

Recent data indicate that secondary causes and a wider range of conditions need to be considered in identifying the underlying causes of hypercholesterolemia, hypertriglyceridemia, hyperalphalipoproteinemia, hypobetalipoproteinemia, and HDL deficiency. Identifying such disorders allows for a more precise assessment of prognosis and the formulation of optimal therapy.

Clinical Utility and Practical Considerations of a Coronary Artery Disease Genetic Risk Score

Background

Coronary artery disease (CAD) risk traditionally has been assessed using clinical risk factors. We evaluated whether molecular genetic markers for CAD risk could add information to traditional variables.

Methods

We developed a false discovery rate 267-marker genetic risk score (FDR₂₆₇) from markers that were significantly associated with CAD in the UK Biobank cohort meta-analysis. FDR₂₆₇ was tested in the Atherosclerosis Risk in Communities cohort using logistic regression and Cox proportional hazards analyses in the European and African American groups.

Results

Our genetic risk score (FDR₂₆₇) was associated with a 1.45 (95% confidence interval, 1.39-1.51) increase in odds ratio and a 1.32 (95% confidence interval, 1.26-1.38) increase in hazard ratio per standard deviation of the score. The score modestly improved the area under the curve (AUC) statistic when added to a clinical model (ΔAUC = 0.0112, P = 0.0002). FDR₂₆₇ predicted incident CAD (C-index = 0.60), although it did not improve on clinical risk factors (ΔAUC = 0.0159, P = 0.0965). Individuals in the top quintile of FDR₂₆₇ genetic risk were at approximately 2-fold increased risk compared with the bottom quintile, which is comparable to risk associated with self-reported family history. The performance of FDR₂₆₇ was less robust in the African American sample.

Conclusions

FDR₂₆₇ is significantly associated with CAD in the European sample, with an effect size comparable to self-reported family history. FDR₂₆₇ discriminated between individuals with and without CAD, but did not improve CAD risk prediction over clinical variables. FDR₂₆₇ was less predictive of CAD risk in African Americans.

Efficacy of Evolocumab in Monogenic vs Polygenic Hypercholesterolemia

Background

Inhibitors of proprotein convertase subtilisin kexin 9 are indicated in Canada for treatment of patients with familial hypercholesterolemia (FH). Classically, FH is considered to be a monogenic condition caused by rare pathogenic mutations; however, some patients have hypercholesterolemia on a polygenic basis. Whether the effect of proprotein convertase subtilisin kexin 9 inhibitor treatment differs between patients with monogenic hypercholesterolemia and patients with polygenic hypercholesterolemia is unclear.

Methods

We performed retrospective chart reviews on patients treated with evolocumab 140 mg subcutaneously biweekly from the Lipid Genetics Clinic, London Health Sciences Centre. Evolocumab-treated patients with hypercholesterolemia were grouped into monogenic or polygenic categories on the basis of their genotype determined by targeted next-generation sequencing. Absolute and relative changes in low-density lipoprotein cholesterol (LDL-C) levels before and after evolocumab treatment were studied.

Results

In 32 patients with monogenic heterozygous FH and 7 patients with polygenic hypercholesterolemia treated with evolocumab, absolute incremental reductions in LDL-C were 2.94 ± 1.22 mmol/L and 3.15 ± 0.90 mmol/L, respectively (P = not significant), whereas percent reductions in LDL-C were 63.9% ± 16.0% and 67.7% ± 20.7%, respectively (P = not significant).

Conclusion

Although the sample size is small, the findings suggest comparable biochemical responsiveness to evolocumab in both monogenic (heterozygous) and polygenic hypercholesterolemia.

Functional polymorphisms of the APOA1/C3/A4/A5-ZPR1-BUD13 gene cluster are associated with dyslipidemia in a sex-specific pattern

Background

Dyslipidemia contributes to the risk of many diseases, including stroke, cardiovascular disease and metabolic-related diseases. Previous studies have indicated that single nucleotide polymorphisms (SNPs) are associated with different levels of serum lipid. Therefore, this study explored the relationship between the APOA1/C3/A4/A5-ZPR1-BUD13 gene cluster gene polymorphisms and dyslipidemia in the total sample population and stratified by genders in a northeast Chinese population.

Methods

A total of 3,850 participants from Jilin Province, China, were enrolled in our study, and their serum lipid levels were measured. Six functional SNPs (APOA1 rs5072, APOC3 rs5128, APOA4 rs5104, APOA5 rs651821, ZPR1 rs2075294 and BUD13 rs10488698) were genotyped using polymerase chain reaction and MALDI-TOF-MS. Logistic regression analysis was performed to explore the relationship of APOA1/C3/A4/A5-ZPR1-BUD13 gene cluster gene polymorphisms with dyslipidemia. Linkage disequilibrium and haplotype analyses were performed with the SNPStats program and Haploview software.

Results

All SNPs conformed to Hardy-Weinberg equilibrium. Logistic regression analysis revealed that rs5072, rs5128 and rs651821 were associated with hypertriglyceridemia, rs5104 and rs651821 were associated with low-HDL cholesterolemia in overall group. rs651821 was associated with hypertriglyceridemia and low-HDL cholesterolemia in both the male and female group. However, among females, rs5072 was observed to be associated with hypertriglyceridemia. Haplotype analysis showed that haplotypes TGCCGC and CAGCGC were associated with dyslipidemia in the overall, male and female groups.

Conclusion

SNPs in the APOA1/C3/A4/A5-ZPR1-BUD13 gene cluster were associated with dyslipidemia. Furthermore, the association of APOA1 rs5072 in this gene cluster with dyslipidemia differed between genders; thus, additional studies are needed to confirm this conclusion, and the mechanisms underlying these results warrant further exploration.

Large-scale deletions of the ABCA1 gene in patients with hypoalphalipoproteinemia

Copy-number variations (CNVs) have been studied in the context of familial hypercholesterolemia but have not yet been evaluated in patients with extreme levels of HDL cholesterol. We evaluated targeted, next-generation sequencing data from patients with very low levels of HDL cholesterol (i.e., hypoalphalipoproteinemia) with the VarSeq-CNV^® caller algorithm to screen for CNVs that disrupted the ABCA1, LCAT, or APOA1 genes. In four individuals, we found three unique deletions in ABCA1: a heterozygous deletion of exon 4, a heterozygous deletion that spanned exons 8 to 31, and a heterozygous deletion of the entire ABCA1 gene. Breakpoints were identified with Sanger sequencing, and the full-gene deletion was confirmed by using exome sequencing and the Affymetrix CytoScan HD array. Previously, large-scale deletions in candidate HDL genes had not been associated with hypoalphalipoproteinemia; our findings indicate that CNVs in ABCA1 may be a previously unappreciated genetic determinant of low levels of HDL cholesterol. By coupling bioinformatic analyses with next-generation sequencing data, we can successfully assess the spectrum of genetic determinants of many dyslipidemias, including hypoalphalipoproteinemia.