Molecular Characterization of Familial Hypercholesterolemia in a North American Cohort

Identification of pathogenic variants in the Brazilian cohort with Familial Hypercholesterolemia using exon-targeted gene sequencing

Familial hypercholesterolemia (FH) is a monogenic disease characterized by high plasma low-density lipoprotein cholesterol (LDL-c) levels and increased risk of premature atherosclerotic cardiovascular disease. Mutations in FH-related genes account for 40% of FH cases worldwide. In this study, we aimed to assess the pathogenic variants in FH-related genes in the Brazilian FH cohort FHBGEP using exon-targeted gene sequencing (ETGS) strategy. FH patients (n=210) were enrolled at five clinical sites and peripheral blood samples were obtained for laboratory testing and genomic DNA extraction. ETGS was performed using MiSeq platform (Illumina). To identify deleterious variants in LDLR, APOB, PCSK9, and LDLRAP1, the long-reads were subjected to Burrows-Wheeler Aligner (BWA) for alignment and mapping, followed by variant calling using Genome Analysis Toolkit (GATK) and ANNOVAR for variant annotation. The variants were further filtered using in-house custom scripts and classified according to the American College Medical Genetics and Genomics (ACMG) guidelines. A total of 174 variants were identified including 85 missense, 3 stop-gain, 9 splice-site, 6 InDel, and 71 in regulatory regions (3'UTR and 5'UTR). Fifty-two patients (24.7%) had 30 known pathogenic or likely pathogenic variants in FH-related genes according to the American College Medical and Genetics and Genomics guidelines. Fifty-three known variants were classified as benign, or likely benign and 87 known variants have shown uncertain significance. Four novel variants were discovered and classified as such due to their absence in existing databases. In conclusion, ETGS and in silico prediction studies are useful tools for screening deleterious variants and identification of novel variants in FH-related genes, they also contribute to the molecular diagnosis in the FHBGEP cohort.

Genetic Testing for Familial Hypercholesterolemia in Clinical Practice

PURPOSE OF REVIEW

Genetic testing has proven utility in identifying and diagnosing individuals with FH. Here we outline the current landscape of genetic testing for FH, recommendations for testing practices and the efforts underway to improve access, availability, and uptake.

RECENT FINDINGS

Alternatives to the traditional genetic testing and counseling paradigm for FH are being explored including expanding screening programs, testing in primary care and/or cardiology clinics, leveraging electronic communication tools like chatbots, and implementing direct contact approaches to facilitate genetic testing of both probands and at-risk relatives. There is no consensus on if, when, and how genetic testing or accompanying genetic counseling should be provided for FH, though traditional genetic counseling and/or testing in specialty lipid clinics is often recommended in expert statements and professional guidelines. More evidence is needed to determine whether alternative approaches to the implementation of genetic testing for FH may be more effective.

Cold shock domain-containing protein E1 is a posttranscriptional regulator of the LDL receptor

The low-density lipoprotein receptor (LDLR) controls cellular delivery of cholesterol and clears LDL from the bloodstream, protecting against atherosclerotic heart disease, the leading cause of death in the United States. We therefore sought to identify regulators of the LDLR beyond the targets of current therapies and known causes of familial hypercholesterolemia. We found that cold shock domain-containing protein E1 (CSDE1) enhanced hepatic LDLR messenger RNA (mRNA) decay via its 3' untranslated region and regulated atherogenic lipoproteins in vivo. Using parallel phenotypic genome-wide CRISPR interference screens in a tissue culture model, we identified 40 specific regulators of the LDLR that were not previously identified by observational human genetic studies. Among these, we demonstrated that, in HepG2 cells, CSDE1 regulated the LDLR at least as strongly as statins and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. In addition, we showed that hepatic gene silencing of Csde1 treated diet-induced dyslipidemia in mice to a similar degree as Pcsk9 silencing. These results suggest the therapeutic potential of targeting CSDE1 to manipulate the posttranscriptional regulation of the LDLR mRNA for the prevention of cardiovascular disease. Our approach of modeling a clinically relevant phenotype in a forward genetic screen, followed by mechanistic pharmacologic dissection and in vivo validation, may serve as a generalizable template for the identification of therapeutic targets in other human disease states.

Health equity in the implementation of genomics and precision medicine: A public health imperative

Recent reviews have emphasized the need for a health equity agenda in genomics research. To ensure that genomic discoveries can lead to improved health outcomes for all segments of the population, a health equity agenda needs to go beyond research studies. Advances in genomics and precision medicine have led to an increasing number of evidence-based applications that can reduce morbidity and mortality for millions of people (tier 1). Studies have shown lower implementation rates for selected diseases with tier 1 applications (familial hypercholesterolemia, Lynch syndrome, hereditary breast and ovarian cancer) among racial and ethnic minority groups, rural communities, uninsured or underinsured people, and those with lower education and income. We make the case that a public health agenda is needed to address disparities in implementation of genomics and precision medicine. Public health actions can be centered on population-specific needs and outcomes assessment, policy and evidence development, and assurance of delivery of effective and ethical interventions. Crucial public health activities also include engaging communities, building coalitions, improving genetic health literacy, and building a diverse workforce. Without concerted public health action, further advances in genomics with potentially broad applications could lead to further widening of health disparities in the next decade.

Improving Familial Hypercholesterolemia Diagnosis Using an EMR-based Hybrid Diagnostic Model

CONTEXT

Familial hypercholesterolemia (FH) confers a greatly increased risk for premature cardiovascular disease, but remains very underdiagnosed and undertreated in primary care populations.

OBJECTIVE

We assessed whether using a hybrid model consisting of 2 existing FH diagnostic criteria coupled with electronic medical record (EMR) data would accurately identify patients with FH in a Midwest US metropolitan healthcare system.

METHODS

We conducted a retrospective, records-based, cross-sectional study using datasets from unique EMRs of living patients. Using Structured Query Language to identify components of 2 currently approved FH diagnostic criteria, we created a hybrid model to identify individuals with FH.

RESULTS

Of 264 264 records analyzed, between 794 and 1571 patients were identified as having FH based on the hybrid diagnostic model, with a prevalence of 1:300 to 1:160. These patients had a higher prevalence of premature coronary artery disease (CAD) (38-58%) than the general population (1.8%) and higher than those having a high CAD risk but no FH (10%). Although most patients were receiving lipid-lowering therapies (LLTs), only 50% were receiving guideline-recommended high-intensity LLT.

CONCLUSION

Using the hybrid model, we identified FH with a higher clinical and genetic detection rate than using standard diagnostic criteria individually. Statin and other LLT use were suboptimal and below guideline recommendations. Because FH underdiagnosis and undertreatment are due partially to the challenges of implementing existing diagnostic criteria in a primary care setting, this hybrid model potentially can improve FH diagnosis and subsequent early access to appropriate treatment.

PCSK9 Gene Participates in the Development of Primary Dyslipidemias

Dyslipidemias are a group of diseases, which are characterized by abnormal blood concentrations of cholesterol, triglycerides and/or low-density lipoprotein-cholesterol (LDL-c). Dyslipidemia is a determinant condition for the progress of an atherosclerotic plaque formation. The resulting atherogenicity is due to at least two mechanisms: first, to the accumulation in the plasma of lipid particles that have the capacity to alter the function of the endothelium and deposit at the atheromatous plaque, and second, at an insufficient concentration of multifactorial type of high density lipoprotein-cholesterol (HDL-c), whose function is to protect against the development of atherosclerosis. Its highest prevalence is encountered among individuals with diabetes, hypertension or overweight. Hyperlipidemia is one of the main predisposing factors for the development of cardiovascular disease. Hyperlipidemia can be the result of a genetic condition, the secondary expression of a primary process or the consequence of exogenous factors (food, cultural, socio-economic, etc.), all of which lead to the elevation of plasma lipid levels. The objective of this study was to carry out an analysis of the genes involved in the development of dyslipidemias that lead to cardiovascular disease with special emphasis on the proprotein convertase subtilin/kexin type 9 (PCSK9) gene. The PCSK9 gene participates in the development of primary dyslipidemias, mainly familial hypercholesterolemia, currently the pharmacological treatment of choice to reduce LDL-c are statins, however, it has been observed that these have been insufficient to eliminate cardiovascular risk, especially in subjects with primary forms of hypercholesterolemia related to genetic mutations, or statin intolerance.

Evinacumab for treatment of familial hypercholesterolemia

Introduction: Familial hypercholesterolemia (FH) is characterized by lifelong elevation of low-density lipoprotein cholesterol (LDL-C), early onset coronary atherosclerosis, and premature death. FH is underdiagnosed and undertreated, but requires aggressive LDL-C-lowering to prevent complications. Current treatment strategies such as lifestyle modification and numerous LDL-C-lowering medications are often insufficient to achieve lipid goals in FH.Areas covered: Angiopoietin-like 3 protein (ANGPTL3) is intricately involved in lipid metabolism. Loss-of-function mutations in ANGPTL3 are associated with panhypolipidemia and reduced coronary atherosclerosis. Evinacumab, a fully human monoclonal antibody, inhibits ANGPTL3 and reduces multiple lipoprotein fractions ~50%, including LDL-C. The use of evinacumab within the FH population is described as well as its regulatory journey to an approved therapeutic.Expert opinion: Evinacumab, with its capacity to lower multiple lipoprotein fractions, particularly LDL-C, independently of LDLR function has potential to revolutionize treatment for FH patients. Current FDA-approval is only for homozygous FH (HoFH), arguably the most impactful indication, but use in other lipid disorders is under investigation. The short-term tolerability of evinacumab is very good, with infrequent, mild, and transient adverse events; however, long-term safety data are needed. The high cost and requirement for intravenous administration may limit adoption of evinacumab, but dramatic LDL-C-lowering and need for new therapeutic options for HoFH will drive interest.

FH through the retrospectoscope

After training as a gastroenterologist in the UK, the author became interested in lipidology while he was a research fellow in the USA and switched careers after returning home. Together with Nick Myant, he introduced the use of plasma exchange to treat familial hypercholesterolemia (FH) homozygotes and undertook non-steady state studies of LDL kinetics, which showed that the fractional catabolic rate of LDL remained constant irrespective of pool size. Subsequent steady-state turnover studies showed that FH homozygotes had an almost complete lack of receptor-mediated LDL catabolism, providing in vivo confirmation of the Nobel Prize-winning discovery by Goldstein and Brown that LDL receptor dysfunction was the cause of FH. Further investigation of metabolic defects in FH revealed that a significant proportion of LDL in homozygotes and heterozygotes was produced directly via a VLDL-independent pathway. Management of heterozygous FH has been greatly facilitated by statins and proprotein convertase subtilisin/kexin type 9 inhibitors but remains dependent upon lipoprotein apheresis in homozygotes. In a recent analysis of a large cohort treated with a combination of lipid-lowering measures, survival was markedly enhanced in homozygotes in the lowest quartile of on-treatment serum cholesterol. Emerging therapies could further improve the prognosis of homozygous FH; whereas in heterozygotes, the current need is better detection.