Comprehensive genotyping in dyslipidemia: mendelian dyslipidemias caused by rare variants and Mendelian randomization studies using common variants

Racial Disparities and Cardiometabolic Risk: New Horizons of Intervention and Prevention

PURPOSE OF REVIEW

Cardiometabolic diseases are a leading cause of morbidity and mortality in the USA and disproportionately impact racial and ethnic minorities. Multiple factors contribute to this disparity including genetic and socioeconomic factors, the latter of which contributes to disparities both through systemic barriers such as healthcare access and by directly impacting metabolism through epigenetics and environment-related alterations in the gut microbiome. This review will discuss advances in medicine that can be used to identify, prognosticate, and treat cardiometabolic diseases, and how these may be used to address existing disparities.

RECENT FINDINGS

There is growing research aimed at identifying novel cardiometabolic disease targets and expanding the use of existing pharmacotherapies based on comorbidities. Advances in metabolomics and genomics can give insight into an individual's unique biochemical profile, providing the means for earlier identification of disease and specific treatment targets. Moreover, developments in telehealth and related medical device technologies can expand access to underserved minority populations and improve control of chronic conditions such as diabetes and hypertension. Precision medicine may be integral to bridging the racial gap in cardiometabolic disease outcomes. Developments in genomics, metabolomics, wearable medical devices, and telehealth can result in personalized treatments for patients that account for the socioeconomic and genetic factors that contribute to poor health outcomes in minorities. As research in this field rapidly progresses, special efforts must be made to ensure inclusion of racial and ethnic minority populations in clinical research and equal access to all treatment modalities.

Effect of Cumulative Exposure to Low-Density Lipoprotein-Cholesterol on Cardiovascular Events in Patients With Familial Hypercholesterolemia

BACKGROUND

Recent studies suggest that cumulative exposure to low-density lipoprotein-cholesterol (LDL-C) leads to the development of atherosclerotic cardiovascular disease (ASCVD). However, few studies have investigated whether this link extends to individuals with familial hypercholesterolemia (FH), a relevant patient population.

METHODS AND RESULTS

We retrospectively investigated the health records of 1,050 patients with clinical FH diagnosis between April 1990 and March 2019. We used Cox proportional hazards models adjusted for established ASCVD risk factors to assess the association between cholesterol-year-score and major adverse cardiovascular events (MACEs), including death from any cause or hospitalization due to ASCVD events. Cholesterol-year-score was calculated as LDL-C max × [age at diagnosis/statin initiation] + LDL-C at inclusion × [age at inclusion - age at diagnosis/statin initiation]. The median follow-up period for MACE evaluation was 12.3 (interquartile range, 9.1-17.5) years, and 177 patients experienced MACEs during the observation period. Cholesterol-year-score was significantly associated with MACEs (hazard ratio, 1.35; 95% confidence interval, 1.07-1.53; P=0.0034, per 1,000 mg-year/dL), independent of other traditional risk factors including age and LDL-C, based on cross-sectional assessment. Cholesterol-year-score improved the discrimination ability of other traditional risk factors for ASCVD events (C-index, 0.901 vs. 0.889; P=0.00473).

CONCLUSIONS

Cumulative LDL-C exposure was strongly associated with MACEs in Japanese patients with FH, warranting early diagnosis and treatment initiation in these patients.

Personalized medicine for cardiovascular diseases

Personalized medicine is an emerging concept involving managing the health of patients based on their individual characteristics, including particular genotypes. Cardiovascular diseases are heritable traits, and family history information is useful for risk prediction. As such, determining genetic information (germline genetic mutations) may also be applied to risk prediction. Furthermore, accumulating evidence suggests that genetic background can provide guidance for selecting effective treatments and preventive strategies in individuals with particular genotypes. These concepts may be applicable both to rare Mendelian diseases and to common complex traits. In this review, we define the concept and provide examples of personalized medicine based on human genetics for cardiovascular diseases, including coronary artery disease, arrhythmia, and cardiomyopathies. We also provide a particular focus on Mendelian randomization studies, especially those examining loss-of function genetic variations, for identifying high-risk individuals, as well as signaling pathways that may be useful targets for improving healthy living without cardiovascular events.

Genomics of hypertriglyceridemia

With regard to heritability of phenotypes, the serum triglyceride level is considered to be highly heritable, with approximately 50% of its variability estimated to derive from parents. Thus, approximately 50% could be modifiable via environmental factors, including lifestyle and medications. Lipoproteins are definitive risk factors for atherosclerotic cardiovascular disease (ASCVD); among these, low-density lipoprotein (LDL) particles have been established as a causal factor for the development of ASCVD. Recently, triglyceride-rich lipoproteins have emerged as additional lipoproteins, which should be considered as residual targets for ASCVD risk reduction by LDL-lowering therapies. Compared with LDL particles, triglyceride-rich lipoproteins are significantly increased in the postprandial state, making it difficult to assess their clinical relevance. However, numerous pieces of evidence suggest that fasting and non-fasting triglycerides are associated with ASCVD. In addition, a recent meta-analysis of a Mendelian randomization study suggests that consideration of apolipoprotein B (APOB) might be better than considering LDL and triglyceride-rich lipoproteins separately. In this review, we examine (1) how triglyceride levels are determined by genetics, (2) lessons from extreme cases exhibiting severe hypertriglyceridemia, and (3) why triglycerides are important, by highlighting clinical and genetic evidence of their associations with ASCVD risk.

Serum Triglycerides and Atherosclerotic Cardiovascular Disease: Insights from Clinical and Genetic Studies

Lipoproteins are a major risk factor for atherosclerotic cardiovascular diseases (ASCVD). Among the lipoproteins, low-density lipoproteins (LDL) have been shown to be causally associated with ASCVD development. In contrast, triglycerides or triglyceride-rich lipoproteins receive less attention than LDL because there is little definite evidence from randomized controlled trials. A Mendelian randomization study has recently been published in which a causal association could be estimated with observational datasets. Using such Mendelian randomization studies, ranging from common to rare genetic variations, triglycerides seem to be causally associated with ASCVD outcomes independent of LDL. Although the “causal association” of serum triglycerides and ASCVD is difficult to assert, accumulated evidence from clinical and Mendelian randomization studies, using common and rare genetic variations, strongly supports such an association. In this article, we provide a summary of investigations focusing on important causal associations between serum triglycerides and ASCVD from the clinical point of view.

Oligogenic familial hypercholesterolemia, LDL cholesterol, and coronary artery disease

BACKGROUND

The genetic background of severe familial hypercholesterolemia (FH) has yet to be determined.

OBJECTIVE

We tested if genetic variants associated with low-density lipoprotein (LDL)-altering autosomal recessive diseases influenced LDL cholesterol levels and the odds for coronary artery disease in patients with high LDL cholesterol.

METHODS

We recruited 500 individuals with elevated LDL cholesterol levels (≥180 mg/dL or ≥140 mg/dL for subjects <15 years). We sequenced the exons of 3 FH genes (LDLR, apolipoprotein B, and proprotein convertase subtilisin/kexin type 9) and 4 LDL-altering accessory genes (ABCG5, ABCG8, APOE, and LDL receptor adaptor protein 1). In addition, 4 single nucleotide polymorphisms associated with polygenic FH in East Asian subjects were genotyped. Oligogenic FH patients were defined as those who harbored damaging variants of both conventional FH genes and LDL-altering accessory genes.

RESULTS

We identified damaging variants of conventional FH genes in 248 participants (50%). We also detected damaging variants in accessory genes in 57 patients (11%) and identified oligogenic FH in 27 of these patients (5%). Polygenic score in the subjects without any FH mutations was significantly higher than those in any other groups. Compared with monogenic FH, oligogenic FH exhibited significantly higher LDL cholesterol (265 mg/dL, 95% confidence interval [CI] 216-312, and 210 mg/dL, 95% CI 189-243; P = .04). Oligogenic FH exhibited higher odds for coronary artery disease when compared with monogenic FH, although it did not reach statistical significance (odds ratio 1.41, 95% CI 0.68-2.21, P = .24).

CONCLUSIONS

Among patients with elevated LDL cholesterol, those with oligogenic FH had higher LDL cholesterol than monogenic FH.

Lipid testing in infectious diseases: possible role in diagnosis and prognosis

INTRODUCTION

Acute infections lead to significant alterations in metabolic regulation including lipids and lipoproteins, which play a central role in the host immune response. In this regard, several studies have investigated the role of lipid levels as a marker of infection severity and prognosis.

SCOPE OF REVIEW

We review here the role of lipids in immune response and the potential mechanisms underneath. Moreover, we summarize studies on lipid and lipoprotein alterations in acute bacterial, viral and parasitic infections as well as their diagnostic and prognostic significance. Chronic infections (HIV, HBV, HCV) are also considered.

RESULTS

All lipid parameters have been found to be significantly dearranged during acute infection. Common lipid alterations in this setting include a decrease of total cholesterol levels and an increase in the concentration of triglyceride-rich lipoproteins, mainly very low-density lipoproteins. Also, low-density lipoprotein cholesterol, apolipoprotein A1, low-density lipoprotein cholesterol and apolipoprotein-B levels decrease. These lipid alterations may have prognostic and diagnostic role in certain infections.

CONCLUSION

Lipid testing may be of help to assess response to treatment in septic patients and those with various acute infections (such as pneumonia, leptospirosis and others). Diagnostically, new onset of altered lipid levels should prompt the clinician to test for underlying infection (such as leishmaniasis).

Clinical Perspectives of Genetic Analyses on Dyslipidemia and Coronary Artery Disease

We have learned that low-density lipoprotein (LDL) cholesterol is the cause of atherosclerosis from various aspects, including a single case with familial hypercholesterolemia, other cases with different types of Mendelian dyslipidemias, large-scale randomized controlled trials using LDL cholesterol lowering therapies, and Mendelian randomization studies using common as well as rare variants associated with LDL cholesterol levels. There is no doubt that determinations of genotypes in lipid-associated genes have contributed not only to the genetic diagnosis for Mendelian dyslipidemias but also to the discoveries of novel therapeutic targets. Furthermore, recent studies have shown that such genetic information could provide useful clues for the risk prediction as well as risk stratification in general and in particular population. We provide the current understanding of genetic analyses relating to plasma lipids and coronary artery disease.