Pathogenic variants in THSD4, encoding the ADAMTS-like 6 protein, predispose to inherited thoracic aortic aneurysm.

PURPOSE: Thoracic aortic aneurysm and dissection (TAAD) is a life-threatening disease with often unrecognized inherited forms. We sought to identify novel pathogenic variants associated with autosomal dominant inheritance of TAAD. METHODS: We analyzed exome sequencing data from 35 French TAAD families and performed next-generation sequencing capture panel of genes in 1114 unrelated TAAD patients. Functional effects of pathogenic variants identified were validated in cell, tissue, and mouse models. RESULTS: We identified five functional variants in THSD4 of which two heterozygous variants lead to a premature termination codon. THSD4 encodes ADAMTSL6 (member of the ADAMTS/L superfamily), a microfibril-associated protein that promotes fibrillin-1 matrix assembly. The THSD4 variants studied lead to haploinsufficiency or impaired assembly of fibrillin-1 microfibrils. Thsd4+/- mice showed progressive dilation of the thoracic aorta. Histologic examination of aortic samples from a patient carrying a THSD4 variant and from Thsd4+/- mice, revealed typical medial degeneration and diffuse disruption of extracellular matrix. CONCLUSION: These findings highlight the role of ADAMTSL6 in aortic physiology and TAAD pathogenesis. They will improve TAAD management and help develop new targeted therapies.

Plasma proprotein-convertase-subtilisin/kexin type 9 (PCSK9) and cardiovascular events in type 2 diabetes.

AIM: To investigate whether plasma concentrations of proprotein-convertase-subtilisin/kexin type 9 (PCSK9) were associated with cardiovascular (CV) events in two cohorts of patients with type 2 diabetes mellitus. METHODS: We considered patients from the DIABHYCAR (n = 3137) and the SURDIAGENE (n = 1468) studies. Baseline plasma PCSK9 concentration was measured using an immunofluorescence assay. In post hoc, but preplanned, analyses we assessed the relationship between PCSK9 and the following endpoints: (1) a combined endpoint of major CV events: CV death, non-fatal myocardial infarction (MI), stroke and heart failure-related hospital admission; (2) a composite of all CV events: MI, stroke, heart failure-related hospital admission, coronary/peripheral angioplasty or bypass, CV death; (3) MI; (4) stroke/transient ischaemic attack (TIA); and (5) CV death. RESULTS: In the DIABHYCAR study, plasma PCSK9 tertiles were associated with the incidence of MI, all CV events and stroke/TIA (P for trend <.05). In adjusted Cox analysis, plasma PCSK9 was associated, independently of classic risk factors, with the incidence of major CV events (hazard ratio [HR] for 1-unit increase of log[PCSK9] 1.28 [95% confidence interval {CI} 1.06-1.55]), the incidence of MI (HR 1.66 [95% CI 1.05-2.63]), and the incidence of all CV events (HR 1.22 [95% CI 1.04-1.44]), but not with CV death. Plasma PCSK9 was not associated with the incidence of CV disease in the participants of the SURDIAGENE study with high CV risk treated with statins and insulin. CONCLUSIONS: We found that PCSK9 was inconsistently associated with CV events in populations with type 2 diabetes. The association may depend on the level of CV risk and the background treatment.

PCSK9 Mutations in Familial Hypercholesterolemia: from a Groundbreaking Discovery to Anti-PCSK9 Therapies.

PURPOSE OF REVIEW: In 2003, Abifadel et al. (Nat. Genet. 34:154-156, 2003) identified PCSK9, encoding proprotein convertase subtilisin/kexin type 9, as the third causal gene for autosomal dominant hypercholesterolemia. This review focuses on the main steps from this major breakthrough in familial hypercholesterolemia (FH) to the latest clinical trials with the anti-PCSK9 antibodies. RECENT FINDINGS: The year 2015 was remarkable in cardiovascular disease through the field of cholesterol. Nearly 30 years after the discovery of statins, a new class of effective lipid-lowering drugs has emerged: the anti-PCSK9 antibodies. The discovery of the first gain-of-function mutations of PCSK9 in FH rapidly became the center of interest of researchers worldwide. Preclinical and clinical studies launched by pharmaceutical companies led to the first three anti-PCSK9 antibodies, two of which (evolocumab and alirocumab) reduce LDL cholesterol levels by 50-60% and received FDA and European Medicines Agency approvals in 2015 on top of statin therapy. Recently, results of the Further Cardiovascular Outcomes Research With PCSK9 Inhibition in Subjects With Elevated Risk (FOURIER) trial, the outcome trial of evolocumab over 2.2 years, showed a reduction of 15-20% in the risk of major cardiovascular outcomes in high-risk patients receiving statin therapy. Results of ODYSSEY OUTCOMES trial, evaluating the effect of alirocumab in 18,000 patients with established CVD are also eagerly awaited in 2018. The evolution of research on PCSK9, starting from the discovery of the first set of mutations in PCSK9 in FH in 2003, is an amazing example of successful translational research. It shows how rigorous and powered genetic analyses can lead to the discovery of a new class of lipid-lowering drugs that give hope in fighting high cholesterol levels and their cardiovascular complications.

Living the PCSK9 adventure: from the identification of a new gene in familial hypercholesterolemia towards a potential new class of anticholesterol drugs.

A decade after our discovery of the involvement of proprotein convertase subtilisin/kexin type 9 (PCSK9) in cholesterol metabolism through the identification of the first mutations leading to hypercholesterolemia, PCSK9 has become one of the most promising targets in cholesterol and cardiovascular diseases. This challenging work in the genetics of hypercholesterolemia paved the way for a plethora of studies around the world allowing the characterization of PCSK9, its expression, its impact on reducing the abundance of LDL receptor, and the identification of loss-of-function mutations in hypocholesterolemia. We highlight the different steps of this adventure and review the published clinical trials especially those with the anti-PCSK9 antibodies evolocumab (AMG 145) and alirocumab (SAR236553/REGN727), which are in phase III trials. The promising results in lowering LDL cholesterol levels raise hope that the PCSK9 adventure will lead, after the large and long-term ongoing phase III studies evaluating efficacy and safety, to a new anticholesterol pharmacological class.

Circulating PCSK9 Linked to Dyslipidemia in Lebanese Schoolchildren.

In adults, elevated levels of circulating Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) have been associated with increased Low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and worse cardiovascular outcomes. However, few studies analyzed the relation between PCSK9 and lipid parameters in pediatric populations. The aim of our study is to evaluate the distribution and the correlation of serum PCSK9 levels with lipid parameters in a sample of Lebanese school children. Using an immunofluorescence assay, we measured serum PCSK9 levels in 681 school children recruited from ten public and private Lebanese schools. We analyzed the association between PCSK9 and age, sex, Body Mass Index (BMI), and lipid parameters (total cholesterol (TC), LDL-C, TG, High-density lipoprotein cholesterol (HDL-C), non-HDL-C, and lipoprotein (a) (Lp(a)). Serum PCSK9 levels were significantly correlated with TC, LDL-C, and non-HDL-C (p value < 0.0001) but not with TG, HDL-C, and Lp(a). PCSK9 levels were also significantly higher in children with high TC, LDL-C, and non-HDL-C (p values = 0.0012, 0.0002, 0.001, respectively). No significant gender differences in PCSK9 were found. In addition, no significant associations between PCSK9 and both age and BMI percentiles were observed. In girls, no difference in PCSK9 values was observed according to menarche while in boys, testosterone levels were not significantly associated with PCSK9. Serum PCSK9 levels were significantly correlated with TC, LDL-C, and non-HDL-C levels. Further studies are needed to find if PCSK9 measurements have an additional value to predict future cardiovascular outcomes in pediatric populations.

Low circulating PCSK9 levels in LPL homozygous children with chylomicronemia syndrome in a syrian refugee family in Lebanon.

Familial chylomicronemia syndrome is a rare autosomal recessive disorder of lipoprotein metabolism characterized by the presence of chylomicrons in fasting plasma and an important increase in plasma triglycerides (TG) levels that can exceed 22.58 mmol/l. The disease is associated with recurrent episodes of abdominal pain and pancreatitis, eruptive cutaneous xanthomatosis, lipemia retinalis, and hepatosplenomegaly. A consanguineous Syrian family who migrated to Lebanon was referred to our laboratory after perceiving familial chylomicronemia syndrome in two children. The LPL and PCSK9 genes were sequenced and plasma PCSK9 levels were measured. Sanger sequencing of the LPL gene revealed the presence of the p.(Val227Phe) pathogenic variant in exon 5 at the homozygous state in the two affected children, and at the heterozygous state in the other recruited family members. Interestingly, PCSK9 levels in homozygous carriers of the p.(Val227Phe) were ≈50% lower than those in heterozygous carriers of the variant (p-value = 0.13) and ranged between the 5th and the 7.5th percentile of PCSK9 levels in a sample of Lebanese children of approximately the same age group. Moreover, this is the first reported case of individuals carrying simultaneously an LPL pathogenic variant and PCSK9 variants, the L10 and L11 leucine insertion, which can lower and raise low-density lipoprotein cholesterol (LDL-C) levels respectively. TG levels fluctuated concomitantly between the two children, were especially high following the migration from a country to another, and were reduced under a low-fat diet. This case is crucial to raise public awareness on the risks of consanguineous marriages to decrease the emergence of inherited autosomal recessive diseases. It also highlights the importance of the early diagnosis and management of these diseases to prevent serious complications, such as recurrent pancreatitis in the case of familial hyperchylomicronemia.

Whole Exome/Genome Sequencing Joint Analysis of a Family with Oligogenic Familial Hypercholesterolemia.

Autosomal Dominant Hypercholesterolemia (ADH) is a genetic disorder caused by pathogenic variants in LDLR, APOB, PCSK9 and APOE genes. We sought to identify new candidate genes responsible for the ADH phenotype in patients without pathogenic variants in the known ADH-causing genes by focusing on a French family with affected and non-affected members who presented a high ADH polygenic risk score (wPRS). Linkage analysis, whole exome and whole genome sequencing resulted in the identification of variants p.(Pro398Ala) in CYP7A1, p.(Val1382Phe) in LRP6 and p.(Ser202His) in LDLRAP1. A total of 6 other variants were identified in 6 of 160 unrelated ADH probands: p.(Ala13Val) and p.(Aps347Asn) in CYP7A1; p.(Tyr972Cys), p.(Thr1479Ile) and p.(Ser1612Phe) in LRP6; and p.(Ser202LeufsTer19) in LDLRAP1. All six probands presented a moderate wPRS. Serum analyses of carriers of the p.(Pro398Ala) variant in CYP7A1 showed no differences in the synthesis of bile acids compared to the serums of non-carriers. Functional studies of the four LRP6 mutants in HEK293T cells resulted in contradictory results excluding a major effect of each variant alone. Within the family, none of the heterozygous for only the LDLRAP1 p.(Ser202His) variant presented ADH. Altogether, each variant individually does not result in elevated LDL-C; however, the oligogenic combination of two or three variants reveals the ADH phenotype.

Identification of a Variant in APOB Gene as a Major Cause of Hypobetalipoproteinemia in Lebanese Families.

Familial hypobetalipoproteinemia (FHBL) is a codominant genetic disorder characterized by reduced plasma levels of low-density lipoprotein cholesterol and apolipoprotein B. To our knowledge, no study on FHBL in Lebanon and the Middle East region has been reported. Therefore, we conducted genetic studies in unrelated families and probands of Lebanese origin presenting with FHBL, in order to identify the causes of this disease. We found that 71% of the recruited probands and their affected relatives were heterozygous for the p.(Arg490Trp) variant in the APOB gene. Haplotype analysis showed that these patients presented the same mutant haplotype. Moreover, there was a decrease in plasma levels of PCSK9 in affected individuals compared to the non-affected and a significant positive correlation between circulating PCSK9 and ApoB levels in all studied probands and their family members. Some of the p.(Arg490Trp) carriers suffered from diabetes, hepatic steatosis or neurological problems. In conclusion, the p.(Arg490Trp) pathogenic variant seems a cause of FHBL in patients from Lebanese origin, accounting for approximately 70% of the probands with FHBL presumably as a result of a founder mutation in Lebanon. This study is crucial to guide the early diagnosis, management and prevention of the associated complications of this disease.

Identification of the first Tangier disease patient in Lebanon carrying a new pathogenic variant in ABCA1.

BACKGROUND: The Middle East region is characterized by low levels of high-density lipoprotein cholesterol (HDL-C). To date, no genetic study has investigated the cause of low HDL-C in the Lebanese population. OBJECTIVE: Our objective was to study the genetic causes for hypoalphalipoproteinemia in a Lebanese family with extremely low HDL-C levels. METHODS: We sequenced the ABCA1 gene and evaluated cholesterol efflux, inflammatory, and metabolic profiles in the proband and his family. RESULTS: We identified the first Lebanese pathogenic variant in ABCA1 gene causing Tangier disease in a consanguineous family. The proband carried a novel homozygous pathogenic variant p.Gly592Asp in exon 14 of ABCA1, which segregated with the disease in the family. Functional study of the p.Gly592Asp pathogenic variant revealed that lipid-free apolipoprotein A-I-dependent cholesterol efflux was completely abolished in cholesterol-loaded human monocytes-derived macrophages isolated from the proband when compared to controls. Systemic inflammatory and metabolic assessments showed that plasma cytokines (MCP-1, MIP-1α, IL-6, CRP, TNF-α), adhesion molecules (ICAM-1, VCAM-1, E-selectin), inflammatory soluble receptors (sIL-6r, sTNFRI, sTNFRII), and metabolic markers (Insulin, C-peptide) were elevated in the proband when compared to controls. Noninvasive cardiovascular investigation revealed the presence of premature artery lesions in the proband. CONCLUSIONS: It is the first case of Tangier disease reported in Lebanon harboring a novel pathogenic variant in ABCA1. Further genetic research is needed in the Middle East where the consanguinity rate is elevated, to understand the cause of the highly prevalent dyslipidemia. This will help guiding the early diagnosis, management, and prevention of cardiovascular complications.

Usefulness of the genetic risk score to identify phenocopies in families with familial hypercholesterolemia?

Familial hypercholesterolemia (FH) is caused by mutations in LDLR (low-density lipoprotein receptor), APOB (apolipoprotein B), PCSK9 (proprotein convertase subtilisin/kexin type 9), or APOE (apolipoprotein E) genes in approximately 80% of the cases. Polygenic forms of hypercholesterolemia may be present among patients clinically diagnosed with FH but with no identified mutation (FH mutation-negative (FH/M-)). To address whether polygenic forms may explain phenocopies in FH families, we calculated a 6-single-nucleotide polymorphism (SNP) genetic risk score (GRS) in all members from five French FH families where a mutation was identified (FH/M+) as well as some phenocopies (FH/M-). In two families, three FH/M- patients present a high GRS suggesting a polygenic hypercholesterolemia for these phenocopies. However, a high GRS is also observed in nine FH/M+ patients and in four unaffected relatives from three families. These observations indicate that the GRS does not seem to be a good diagnostic tool at the individual level. Nevertheless, the GRS seems to be a contributor of the severity of hypercholesterolemia since patients who cumulate a mutation and a high GRS exhibit higher low-density lipoprotein cholesterol levels when compared to patients with only FH (p = 0.054) or only polygenic hypercholesterolemia (p = 0.0039). In conclusion, the GRS can be used as a marker of the severity of hypercholesterolemia but does not seem to be a reliable tool to distinguish phenocopies within FH families.

New Sequencing technologies help revealing unexpected mutations in Autosomal Dominant Hypercholesterolemia.

Autosomal dominant hypercholesterolemia (ADH) is characterized by elevated LDL-C levels leading to coronary heart disease. Four genes are implicated in ADH: LDLR, APOB, PCSK9 and APOE. Our aim was to identify new mutations in known genes, or in new genes implicated in ADH. Thirteen French families with ADH were recruited and studied by exome sequencing after exclusion, in their probands, of mutations in the LDLR, PCSK9 and APOE genes and fragments of exons 26 and 29 of APOB gene. We identified in one family a p.Arg50Gln mutation in the APOB gene, which occurs in a region not usually associated with ADH. Segregation and in-silico analysis suggested that this mutation is disease causing in the family. We identified in another family with the p.Ala3396Thr mutation of APOB, one patient with a severe phenotype carrying also a mutation in PCSK9: p.Arg96Cys. This is the first compound heterozygote reported with a mutation in APOB and PCSK9. Functional studies proved that the p.Arg96Cys mutation leads to increased LDL receptor degradation. This work shows that Next-Generation Sequencing (exome, genome or targeted sequencing) are powerful tools to find new mutations and identify compound heterozygotes, which will lead to better diagnosis and treatment of ADH.

Proprotein convertase subtilisin / kexin 9 (PCSK9) inhibitors and the future of dyslipidemia therapy: an updated patent review (2011-2015).

INTRODUCTION: The identification by Abifadel et al. in 2003 of the first mutations of PCSK9 was the major breakthrough in the cholesterol field that led to a new therapeutic target. This discovery paved the way to new lipid lowering drugs reducing LDL-cholesterol levels through the inhibition of PCSK9. Two anti-PCSK9 monoclonal antibodies have received FDA and EMA approvals: Alirocumab and Evolocumab. Areas covered: This article reviews the different strategies that are pursued to modulate the functional activity of PCSK9 for lowering LDL-cholesterol levels. It also provides a brief overview of the patents related to PCSK9 from 2011 until the end of 2015. This review is addressed to researchers from academia and pharmaceutical companies who are engaged in PCSK9 research/cholesterol regulation. Readers will gain an up-to-date overview of the different strategies that have been investigated to reduce PCSK9, focusing on anti-PCSK9 monoclonal antibodies and the related clinical trials. Expert opinion: Anti-PCSK9 antibodies are a new class of lipid lowering drugs with promising results in reducing LDL-cholesterol. Long-term ongoing studies investigating on a large scale the efficacy and safety of the anti-PCSK9 antibodies and their cardiovascular outcomes are eagerly awaited.