Autosomal recessive hypercholesterolaemia in Sardinia, Italy, and mutations in ARH: a clinical and molecular genetic analysis

Associations of Blood Lipid-Related Polygenic Scores, Lifestyle Factors and Their Combined Effects with Risk of Coronary Artery Disease in the UK Biobank Cohort

Circulating lipids play a crucial role in the development of coronary artery disease (CAD). However, it is unclear whether the genetic susceptibility to hyperlipidemia may interact with lifestyle factors in CAD risk. Using UK Biobank data from 328,606 participants, we evaluated combined effects of genetic susceptibility to hyperlipidemia and lifestyle factors with risk of CAD. We found that both blood lipid-related polygenic score (PGS) and healthy lifestyle score (HLS) are independently associated with CAD risk, and individuals with the highest-risk lipid-related PGS and the least healthy HLS had the highest CAD risk. This association was stronger in younger (< 60 years, hazard ratio: 4.46, 95% confidence interval: 3.44-5.78) than older adults (2.54, 2.13-3.03). Our study suggests that individuals, particularly younger adults, with higher-risk PGSs of blood lipid traits would benefit more substantially by adherence to a healthy lifestyle than those with lower PGSs.

Consensus document on diagnosis and management of familial hypercholesterolemia from the Italian Society for the Study of Atherosclerosis (SISA)

AIMS

Familial Hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism that causes an increased risk of premature atherosclerotic cardiovascular disease (ASCVD). Although early diagnosis and treatment of FH can significantly improve the cardiovascular prognosis, this disorder is underdiagnosed and undertreated. For these reasons the Italian Society for the Study of Atherosclerosis (SISA) assembled a Consensus Panel with the task to provide guidelines for FH diagnosis and treatment.

DATA SYNTHESIS

Our guidelines include: i) an overview of the genetic complexity of FH and the role of candidate genes involved in LDL metabolism; ii) the prevalence of FH in the population; iii) the clinical criteria adopted for the diagnosis of FH; iv) the screening for ASCVD and the role of cardiovascular imaging techniques; v) the role of molecular diagnosis in establishing the genetic bases of the disorder; vi) the current therapeutic options in both heterozygous and homozygous FH. Treatment strategies and targets are currently based on low-density lipoprotein cholesterol (LDL-C) levels, as the prognosis of FH largely depends on the magnitude of LDL-C reduction achieved by lipid-lowering therapies. Statins with or without ezetimibe are the mainstay of treatment. Addition of novel medications like PCSK9 inhibitors, ANGPTL3 inhibitors or lomitapide in homozygous FH results in a further reduction of LDL-C levels. LDL apheresis is indicated in FH patients with inadequate response to cholesterol-lowering therapies.

CONCLUSION

FH is a common, treatable genetic disorder and, although our understanding of this disease has improved, many challenges still remain with regard to its identification and management.

Novel Finnish-enriched variants causing severe hypercholesterolemia and their clinical impact on coronary artery disease

BACKGROUND AND AIMS

Severe hypercholesterolemia (LDL-cholesterol ≥ 5 mmol/l) is a major risk factor for coronary artery disease (CAD). The etiology incudes both genetic and nongenetic factors, but persons carrying mutations in known hypercholesterolemia-associated genes are at significantly higher CAD risk than non-carriers. Yet, a significant proportion of mutation carriers remains undetected while the assessment of genetic candidate variants in clinical practice is challenging.

METHODS

To address these challenges, we set out to test the utility of a practical approach to leverage data from a large reference cohort, the FinnGen Study encompassing 356,082 persons with extensive longitudinal health record information, to aid the clinical evaluation of single genetic candidate genes variants detected by exome sequence analysis in a target population of 351 persons with severe hypercholesterolemia.

RESULTS

We identified 23 rare missense mutations in known hypercholesterolemia genes, 3 of which were previously described mutations (LDLR Pro309Lysfs, LDLR Arg595Gln and APOB Arg3527Gln). Subsequent in silico and clinical assessment of the remaining 20 variants pinpointed two likely hypercholesterolemia-associated variants in LDLR (Arg574Leu and Glu626Lys) and one in LDLRAP1 (Arg151Trp). Heterozygous carriers of the novel LDLR and LDLRAP1 variants received statin treatment more often than non-carriers (OR 2.1, p = 1.8e-6 and OR 1.4, p = 0.001) and untreated carriers had higher risk for ischemic heart disease (OR 2.0, p = 0.03 and OR 1.8, p = 0.008).

CONCLUSIONS

Our data elucidate the wide spectrum of genetic variants impacting hypercholesterolemia and demonstrate the utility of a large reference population to assess the heterogeneous impact of candidate gene variants on cardiovascular disease risk.

Current Data and New Insights into the Genetic Factors of Atherogenic Dyslipidemia Associated with Metabolic Syndrome

Atherogenic dyslipidemia plays a critical role in the development of metabolic syndrome (MetS), being one of its major components, along with central obesity, insulin resistance, and hypertension. In recent years, the development of molecular genetics techniques and extended analysis at the genome or exome level has led to important progress in the identification of genetic factors (heritability) involved in lipid metabolism disorders associated with MetS. In this review, we have proposed to present the current knowledge related to the genetic etiology of atherogenic dyslipidemia, but also possible challenges for future studies. Data from the literature provided by candidate gene-based association studies or extended studies, such as genome-wide association studies (GWAS) and whole exome sequencing (WES,) have revealed that atherogenic dyslipidemia presents a marked genetic heterogeneity (monogenic or complex, multifactorial). Despite sustained efforts, many of the genetic factors still remain unidentified (missing heritability). In the future, the identification of new genes and the molecular mechanisms by which they intervene in lipid disorders will allow the development of innovative therapies that act on specific targets. In addition, the use of polygenic risk scores (PRS) or specific biomarkers to identify individuals at increased risk of atherogenic dyslipidemia and/or other components of MetS will allow effective preventive measures and personalized therapy.

Deletion of LDLRAP1 Induces Atherosclerotic Plaque Formation, Insulin Resistance, and Dysregulated Insulin Response in Adipose Tissue

Dyslipidemia, vascular inflammation, obesity, and insulin resistance often overlap and exacerbate each other. Mutations in low density lipoprotein receptor adaptor protein-1 (LDLRAP1) lead to LDLR malfunction and are associated with the autosomal recessive hypercholesterolemia disorder in humans. However, direct causality on atherogenesis in a defined preclinical model has not been reported. The objective of this study was to test the hypothesis that deletion of LDLRAP1 will lead to hypercholesteremia and atherosclerosis. LDLRAP1^-/- mice fed a high-fat Western diet had significantly increased plasma cholesterol and triglyceride concentrations accompanied with significantly increased plaque burden compared with wild-type controls. Unexpectedly, LDLRAP1^-/- mice gained significantly more weight compared with controls. Even on a chow diet, LDLRAP1^-/- mice were insulin-resistant, and calorimetric studies suggested an altered metabolic profile. The study showed that LDLRAP1 is highly expressed in visceral adipose tissue, and LDLRAP1^-/- adipocytes are significantly larger, have reduced glucose uptake and AKT phosphorylation, but have increased CD36 expression. Visceral adipose tissue from LDLRAP1^-/- mice was hypoxic and had gene expression signatures of dysregulated lipid storage and energy homeostasis. These data are the first to indicate that lack of LDLRAP1 directly leads to atherosclerosis in mice and also plays an unanticipated metabolic regulatory role in adipose tissue. LDLRAP1 may link atherosclerosis and hypercholesterolemia with common comorbidities of obesity and insulin resistance.

Etiologic Puzzle of Coronary Artery Disease: How Important Is Genetic Component?

In the modern era, coronary artery disease (CAD) has become the most common form of heart disease and, due to the severity of its clinical manifestations and its acute complications, is a major cause of morbidity and mortality worldwide. The phenotypic variability of CAD is correlated with the complex etiology, multifactorial (caused by the interaction of genetic and environmental factors) but also monogenic. The purpose of this review is to present the genetic factors involved in the etiology of CAD and their relationship to the pathogenic mechanisms of the disease. Method: we analyzed data from the literature, starting with candidate gene-based association studies, then continuing with extensive association studies such as Genome-Wide Association Studies (GWAS) and Whole Exome Sequencing (WES). The results of these studies revealed that the number of genetic factors involved in CAD etiology is impressive. The identification of new genetic factors through GWASs offers new perspectives on understanding the complex pathophysiological mechanisms that determine CAD. In conclusion, deciphering the genetic architecture of CAD by extended genomic analysis (GWAS/WES) will establish new therapeutic targets and lead to the development of new treatments. The identification of individuals at high risk for CAD using polygenic risk scores (PRS) will allow early prophylactic measures and personalized therapy to improve their prognosis.

Patient-Specific Induced Pluripotent Stem Cell-Derived Hepatocyte-Like Cells as a Model to Study Autosomal Recessive Hypercholesterolemia

Autosomal recessive hypercholesterolemia (ARH) is a rare monogenic disorder caused by pathogenic variants in the low-density lipoprotein receptor (LDLR) adaptor protein 1 (LDLRAP1) gene, encoding for the LDLRAP1 protein, which impairs internalization of hepatic LDLR. There are variable responses of ARH patients to treatment and the pathophysiological mechanism(s) for this variability remains unclear. This is in part caused by absence of reliable cellular models to evaluate the effect of LDLRAP1 mutations on the LDLRAP1 protein function and its role in LDLR internalization. Here, we aimed to validate patient-specific induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (HLCs) as an appropriate tool to model ARH disease. Fibroblasts from an ARH patient carrying the recently reported nonsense mutation, c.649G>T, were reprogrammed into hiPSCs using Sendai viral vectors. In addition, we used clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to create an LDLRAP1 gene (also known as ARH) knockout in two different human iPSC lines. ARH patient-derived iPSCs, ARH-knockout iPSC lines, and control iPSCs were efficiently differentiated into HLCs. Western blot analysis demonstrated the absence of LDLRAP1 in HLCs derived from patient and knockout iPSCs, and this was associated with a decreased low-density lipoprotein cholesterol (LDL-C) uptake in ARH-mutant/knockout HLCs compared to control HLCs. In conclusion, we determined that the recently described c.649G>T point mutation in LDLRAP1 induces absence of the LDLRAP1 protein, similar to what is seen following LDLRAP1 knockout. This causes a decreased, although not fully absent, LDL-uptake in ARH-mutant/knockout HLCs. As knockout of LDLRAP1 or presence of the c.649G>T point mutation results in absence of LDLRAP1 protein, residual LDL uptake might be regulated by LDLRAP1-independent internalization mechanisms. Patient-specific iPSC-derived HLCs can therefore be a powerful tool to further decipher LDLRAP1 mutations and function of the protein.

Persistent hypercholesterolemia in child with homozygous autosomal recessive hypercholesterolemia: A decade of lipid management

Autosomal recessive hypercholesterolemia (ARH) is a rare form of genetic hypercholesterolemia caused by mutations in low density lipoprotein receptor adaptor protein 1 (LDLRAP1). The proband first presented with linear eruptive xanthomas over her ankles, knees and elbows, with low density lipoprotein cholesterol (LDL-C) of 16.0 mmol/L (618.7 mg/dL), at 2.5 years old. Next generation sequencing revealed a novel homozygous mutation in LDLRAP1 exon 5 (c.466delG). In the first year, drug regimens of either cholestyramine or simvastatin, reduced her LDL-C to 10.5 mmol/L (406 mg/dL) and 11.7 mmol/L (452.4 mg/dL), respectively. Combination simvastatin and ezetimibe was the mainstay of therapy from age 5 - 10 years. Her lowest achieved LDL-C was 6.3 mmol/L (243.6 mg/dL). Switching to atorvastatin did not lead to further reduction. Carotid intima-media thickness was 0.47 mm (> 97^th percentile) and 0.32 mm (75 - 95^th percentile) at ages 8 years and 11 years, respectively. Addition of monthly injections of evolocumab for 3 months, led to an increase in LDL-C, from 7.0 mmol/L (270.7 mg/dL) to a range of [(8.4 - 9.1) mmol/L or (324.8 - 351.9) mg/dL]. In this report, a decade-long lipid management is described in a patient with ARH. Residual activity of LDLRAP1 is a likely determinant of her response. Clinical management remains sub-optimal and options for the paediatric population are limited. Novel classes of cholesterol-lowering medications are needed for this ultra-rare and severe hypercholesterolemia.

Homozygous autosomal recessive hypercholesterolaemia in a South Asian child presenting with multiple cutaneous xanthomata

Autosomal recessive hypercholesterolemia (ARH; OMIM #603813) is an extremely rare disorder of lipid metabolism caused by loss-of-function variants in the LDL receptor adapter protein 1 (LDLRAP1) gene, which is characterized by severe hypercholesterolaemia and an increased risk of premature atherosclerotic cardiovascular disease. We report the case of an 11-year-old girl who presented with multiple painless yellowish papules around her elbows and knees of two-year duration. She had been reviewed by several general practitioners, with some of the papules having been excised, but without a specific diagnosis being made. The child was referred to a paediatric service for further evaluation and treatment of the cutaneous lesions, which appeared xanthomatous in nature. A lipid profile showed severe hypercholesterolaemia. Next generation sequencing analysis of a monogenic hypercholesterolaemia gene panel revealed homozygosity for a pathogenic frameshift mutation, c.71dupG, p.Gly25Argfs*9 in LDLRAP1. Her parents and brother, who were asymptomatic, were screened and found to be heterozygous carriers of the LDLRAP1 variant. There was no known consanguinity in the family. She was commenced on the HMG-CoA reductase inhibitor, atorvastatin, to good effect, with a ∼76% reduction in LDL-cholesterol at a dose of 50 mg per day. At six-month follow-up, there had been no obvious regression of the xanthomata, but importantly, no enlargement of, or the development of new papular lesions, have occurred. In summary, we report a child who presented with multiple cutaneous xanthomata and was confirmed to have ARH by the presence of a homozygous novel pathogenic frameshift variant in LDLRAP1.

Genetics of Familial Hypercholesterolemia: New Insights

Familial hypercholesterolemia (FH) is one of the most common monogenic diseases, leading to an increased risk of premature atherosclerosis and its cardiovascular complications due to its effect on plasma cholesterol levels. Variants of three genes (LDL-R, APOB and PCSK9) are the major causes of FH, but in some probands, the FH phenotype is associated with variants of other genes. Alternatively, the typical clinical picture of FH can result from the accumulation of common cholesterol-increasing alleles (polygenic FH). Although the Czech Republic is one of the most successful countries with respect to FH detection, approximately 80% of FH patients remain undiagnosed. The opportunities for international collaboration and experience sharing within international programs (e.g., EAS FHSC, ScreenPro FH, etc.) will improve the detection of FH patients in the future and enable even more accessible and accurate genetic diagnostics.

Autosomal recessive hypercholesterolemia in a kindred of Syrian ancestry

Autosomal recessive hypercholesterolemia is a rare genetic disorder due to homozygosity or compound heterozygosity for mutations in the low-density lipoprotein receptor adapter protein 1 gene (LDLRAP1), resulting in elevated low-density lipoprotein cholesterol (LDL-C) levels, large xanthomas, and increased cardiovascular risk. Here, we describe a Danish family of Syrian ancestry carrying a frameshift mutation in LDLRAP1, previously only described in Sardinia and Sicily in Italy and in Spain. In 2 children homozygous for this mutation, we evaluate the effect of long-term lipid-lowering treatment with atorvastatin as monotherapy or in combination with ezetimibe. At referral to the lipid clinic at Viborg Regional Hospital, 3 of 4 children had LDL-C levels of 468, 538, and 371 mg/dL, respectively, with 1 child already showing cutaneous xanthomas at 10 years of age. For comparison, the fourth child and the parents had LDL-C levels of 85, 116, and 124 mg/dL. Genetic testing revealed that all 3 children with severely elevated LDL-C were homozygous for a rare frameshift mutation in LDLRAP1, p.His144GlnfsTer27 (c.431dupA), whereas the fourth child and both parents were heterozygous for this mutation. Lipid-lowering treatment was started in the 2 oldest children (at 10 and 7 years of age). Atorvastatin (40 mg/d) combined with ezetimibe (10 mg/d) reduced LDL-C by 75% in the first child and resulted in near-complete regression of xanthomas. In the second child, atorvastatin (40 mg/d) as monotherapy reduced LDL-C by 61%. Both regimens were superior to treatment with pravastatin as monotherapy (20 mg/d) and to pravastatin in combination with cholestyramine (2 g twice daily). High-intensity statin therapy alone or in combination with ezetimibe resulted in marked reductions in LDL-C in 2 children homozygous for a rare frameshift mutation in LDLRAP1 and lead to regression of large xanthomas.

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.

Regulation of glucose and lipid metabolism in health and disease

Glucose and fatty acids are the major sources of energy for human body. Cholesterol, the most abundant sterol in mammals, is a key component of cell membranes although it does not generate ATP. The metabolisms of glucose, fatty acids and cholesterol are often intertwined and regulated. For example, glucose can be converted to fatty acids and cholesterol through de novo lipid biosynthesis pathways. Excessive lipids are secreted in lipoproteins or stored in lipid droplets. The metabolites of glucose and lipids are dynamically transported intercellularly and intracellularly, and then converted to other molecules in specific compartments. The disorders of glucose and lipid metabolism result in severe diseases including cardiovascular disease, diabetes and fatty liver. This review summarizes the major metabolic aspects of glucose and lipid, and their regulations in the context of physiology and diseases.

A new variant (c.1A>G) in LDLRAP1 causing autosomal recessive hypercholesterolemia: Characterization of the defect and response to PCSK9 inhibition

BACKGROUND AND AIMS

Autosomal recessive hypercholesterolemia (ARH) is a rare disorder caused by mutations in LDLRAP1, which impairs internalization of hepatic LDL receptor (LDLR). ARH patients respond relatively well to statins or the combination of statins and Ezetimibe, but scarce and variable data on treatment with PCSK9 inhibitors is available. We aimed to identify and characterize the defect in a hypercholesterolemic patient with premature cardiovascular disease and determine the response to lipid-lowering treatment.

METHODS AND RESULTS

Gene sequencing revealed a homozygous c.1A > G:p.? variant in LDLRAP1. Primary lymphocytes were isolated from the ARH patient, one control and two LDLR-defective subjects, one LDLR:p.(Cys352Ser) heterozygote and one LDLR:p.(Asn825Lys) homozygote. The patient had undetectable full-length ARH protein by Western blotting, but expressed a lower-than-normal molecular weight peptide. LDLR activity was measured by flow cytometry, which showed that LDL binding and uptake were reduced in lymphocytes from the ARH patient as compared to control lymphocytes, but were slightly higher than in those from the LDLR:p.(Cys352Ser) heterozygote. Despite the analogous internalization defect predicted in ARH and homozygous LDLR:p.(Asn825Lys) lymphocytes, LDL uptake was higher in the former than in the latter. LDL-cholesterol levels were markedly reduced by the successive therapy with Atorvastatin and Atorvastatin plus Ezetimibe, and the addition of Evolocumab biweekly decreased LDL-cholesterol by a further 39%.

CONCLUSIONS

The LDLRAP1:c.1A > G variant is associated with the appearance of an N-terminal truncated ARH protein and to reduced, although still significant, LDLR activity in lymphocytes. Residual LDLR activity may be relevant for the substantial response of the patient to Evolocumab.

A case of autosomal recessive hypercholesterolemia caused by a new variant in the LDL receptor adaptor protein 1 gene

We report a new variant in the LDLRAP1 gene associated with autosomal recessive hypercholesterolemia in a woman of central European ancestry.

Ischemic Heart Disease in Subjects of Young Age: Current State of the Problem. Features of Etiology, Clinical Manifestation and Prognosis

In addition to conventional risk factors in young patients with ischemic heart disease (IHD) numerous other risk factors including genetics play an important role in its causation. Molecular genetic testing is recommended for the detection of monogenic diseases with a high risk of developing IHD, such as familial hypercholesterolemia. In majority ofyoung patients, the first manifestation of IHD is an acute coronary syndrome. Young patients with IHD more often have normal coronary arteries or single-vessel coronary disease, and in up to 20% of them cause of myocardial ischemia is not related to atherosclerosis. In general, young patients with IHD have better prognosis. However, there are sex differences in IHD outcomes the prognosis of patients with premature IHD and reason for this is still unclear.

[Diagnosis and Treatment of Familial Hypercholesterolemia]

Diagnosis and Treatment of Familial Hypercholesterolemia Abstract. Familial hypercholesterolemia secondary to heterozygous mutations in the LDL receptor, Apolipoprotein B or PCSK9 gene is characterized by 2- to 3-fold elevated LDL cholesterol levels, premature atherosclerosis and extravascular cholesterol deposits (tendon xanthomata, corneal arcus). The same phenotype may occur if a person carries several LDL cholesterol rising polymorphisms (polygenic FH). Primary prevention with statins has been shown to dramatically reduce the cardiovascular burden in patients with the disease. However, it is estimated that less than 10 % of affected subjects in Switzerland have received the diagnosis, and undertreatment is frequent. Thus, clinical cardiovascular events are still the first manifestation of the disease in many cases. A correct diagnosis in index patients and cascade screening of families are mandatory to identify and treat patients before they suffer the sequelae of untreated severe hypercholesterolemia. In patients with clinical cardiovascular disease combination lipid lowering treatment with potent statins, ezetimibe and the newly available PCSK9 inhibitors will successfully lower LDL cholesterol to normal or even target levels.

Case reports of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition nonresponse

Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors, a novel class of monoclonal antibodies, reduces low-density lipoprotein cholesterol levels and improves cardiovascular outcomes. Given the short time frame, these agents have been available for use; reports of nonresponse to the PCSK9 inhibitor therapy are scarce in literature. We describe 2 cases with substantially lesser than expected low-density lipoprotein cholesterol lowering on PCSK9 therapy. Nonresponse to PCSK9 inhibition was attributed to autosomal recessive hypercholesterolemia (secondary to low-density lipoprotein receptor adaptor protein 1 mutation) and plasmapheresis after PCSK9 inhibitor drug injections. Additional PCSK9 inhibitor nonresponders are likely to emerge as the use of these agents increases overtime.

Autosomal recessive hypercholesterolemia in Spain

BACKGROUND AND AIMS

Autosomal recessive hypercholesterolemia (ARH) is a very rare disease, caused by mutations in LDL protein receptor adaptor 1 (LDLRAP1). It is characterized by high levels of low-density lipoprotein cholesterol (LDL-C) and increased risk of premature cardiovascular disease. We aimed to characterize ARH in Spain.

METHODS

Data were collected from the Dyslipidemia Registry of the Spanish Atherosclerosis Society. A literature search was performed up to June 2017, and all diagnostic genetic studies for familial hypercholesterolemia of Spain were reviewed.

RESULTS

Seven patients with ARH were identified, 6 true homozygous and one compound heterozygous with a novel mutation: c.[863C>T];p.[Ser288Leu]. High genetic heterogeneity was found in this cohort. True homozygous subjects for LDLRAP1 have more severe phenotypes than the compound heterozygous patient, but similar to patients with homozygous familial hypercholesterolemia (HoFH). Cardiovascular disease was present in 14% of the ARH patients. LDL-C under treatment was above 185 mg/dl and the response to PCSK9 inhibitors was heterogeneous. Finally, the estimated prevalence in Spain is very low, with just 1 case per 6.5 million people.

CONCLUSIONS

ARH is a very rare disease in Spain, showing high genetic heterogeneity, similarly high LDL-C concentrations, but lower incidence of ASCVD than HoFH.

Autosomal Recessive Hypercholesterolemia: Long-Term Cardiovascular Outcomes

BACKGROUND

Autosomal recessive hypercholesterolemia (ARH) is a rare lipid disorder characterized by premature atherosclerotic cardiovascular disease (ASCVD). There are sparse data for clinical management and cardiovascular outcomes in ARH.

OBJECTIVES

Evaluation of changes in lipid management, achievement of low-density lipoprotein cholesterol (LDL-C) goals and cardiovascular outcomes in ARH.

METHODS

Published ARH cases were identified by electronic search. All corresponding authors and physicians known to treat these patients were asked to provide follow-up information, using a standardized protocol.

RESULTS

We collected data for 52 patients (28 females, 24 males; 31.1 ± 17.1 years of age; baseline LDL-C: 571.9 ± 171.7 mg/dl). During a mean follow-up of 14.1 ± 7.3 years, there was a significant increase in the use of high-intensity statin and ezetimibe in combination with lipoprotein apheresis; in 6 patients, lomitapide was also added. Mean LDL-C achieved at nadir was 164.0 ± 85.1 mg/dl (-69.6% from baseline), with a better response in patients taking lomitapide (-88.3%). Overall, 23.1% of ARH patients reached LDL-C of <100 mg/dl. During follow-up, 26.9% of patients had incident ASCVD, and 11.5% had a new diagnosis of aortic valve stenosis (absolute risk per year of 1.9% and 0.8%, respectively). No incident stroke was observed. Age (≥30 years) and the presence of coronary artery disease at diagnosis were the major predictors of incident ASCVD.

CONCLUSIONS

Despite intensive treatment, LDL-C in ARH patients remains far from targets, and this translates into a poor long-term cardiovascular prognosis. Our data highlight the importance of an early diagnosis and treatment and confirm the fact that an effective treatment protocol for ARH is still lacking.

Genetic epidemiology of autosomal recessive hypercholesterolemia in Sicily: Identification by next-generation sequencing of a new kindred

BACKGROUND

Autosomal recessive hypercholesterolemia (ARH) is a rare inherited lipid disorder. In Sardinia, differently from other world regions, the mutated allele frequency is high. It is caused by mutations in the low-density lipoprotein receptor adaptor protein 1 gene. Fourteen different mutations have been reported so far; in Sardinia, 2 alleles (ARH1 and ARH2) explain most of the cases. Four ARH patients, all carriers of the ARH1 mutation, have been identified in mainland Italy and 2 in Sicily.

OBJECTIVE

The objectives of the study were to improve the molecular diagnosis of familial hypercholesterolemia (FH) and to estimate the frequency of the ARH1 allele in 2 free-living Sicilian populations.

METHODS

We sequenced by targeted next-generation sequencing 20 genes related to low-density lipoprotein metabolism in 50 hypercholesterolemic subjects. Subjects from 2 free-living populations from Northern (Ventimiglia Heart Study, 848 individuals) and Southern Sicily (Zabut Zabùt Aging Project, 1717 individuals) were genotyped for ARH1 allele.

RESULTS

We identified 1 homozygous carrier of the ARH1 mutation among the 50 hypercholesterolemic outpatients. Population-based genotyping of ARH1 in 2565 subjects allowed the identification of 1 heterozygous carrier. The overall estimated allele frequency of ARH1 in Sicily was 0.0002 (0.02%).

CONCLUSIONS

The identification of a new case of ARH in Sicily among 50 clinically diagnosed FH highlights the importance of next-generation sequencing analysis as tool to improve the FH diagnosis. Our results also indicate that ARH1 carrier status is present in ∼1:2500 of Sicilian inhabitants, confirming that ARH is extremely rare outside Sardinia.

Efficacy of Lomitapide in the Treatment of Familial Homozygous Hypercholesterolemia: Results of a Real-World Clinical Experience in Italy

INTRODUCTION

Homozygous familial hypercholesterolaemia (HoFH) is a rare form of inherited dyslipidemia resistant to conventional cholesterol-lowering medications so that lipoprotein apheresis (LA) is usually required. Lomitapide has been approved for the treatment of HoFH. The aim of this study was to evaluate the benefits of lomitapide in HoFH patients followed with the usual clinical care.

METHODS

Clinical and biochemical data were retrospectively collected in 15 HoFH patients (10 with mutations in the LDLR gene and 5 in the LDLRAP1 gene) treated for at least 6 months with lomitapide in addition to lipid-lowering therapies (LLT) in different Lipid Clinics across Italy.

RESULTS

The mean follow-up period was 32.3 ± 29.7 months. During background therapies, HoFH patients showed a mean LDL-C level of 426.0 ± 204.0 mg/dl. The addition of lomitapide at the average dosage of 19 mg/day lowered LDL-C levels by 68.2 ± 24.8%. At their last visit, 60% of patients showed LDL-C <100 mg/dl and 46.6% <70 mg/dl. During follow-up, 8 of 10 patients receiving LA (80%) stopped this treatment due to marked LDL-C reduction. A wide range (13-95%) of individual LDL-C reduction was observed, but this was not related to genotype. During follow-up, 53.3% of patients reported at least one episode of diarrhea, but none was referred as severe; none had liver transaminase >5× ULN or had to stop treatment due to side effects. A subset of patients was evaluated by liver ultrasound and fibroscan (n = 5) or nuclear magnetic resonance with spectroscopy (MRS) (n = 1) not showing clinical evidence of liver damage.

CONCLUSION

In this real-world experience, lomitapide was confirmed to be a very powerful cholesterol-lowering agent in HoFH showing a good safety profile.

Using human genetics to discover new therapeutic targets for plasma lipids

Genetic variation arises through multiple different alleles that vary in frequency and severity of effect. Mutations that give rise to Mendelian disorders, such as the LDL receptor (LDLR) mutations that result in familial hypercholesterolaemia, are efficiently winnowed from the population by purifying selection and are almost inevitably rare. Conversely, alleles that are common in the population (such that homozygotes for the minor allele are present even in modest sample sizes) typically have very modest phenotypic effects. Mutations in the gene for proprotein convertase subtilisin/kexin type 9 (PCSK9) represent an unusual but informative exception in that they are relatively common but have large effects on phenotype. Loss-of-function mutations in PCSK9 occur in ~2.5% of African Americans and are associated with large reductions in coronary heart disease (CHD) risk. The development of agents to inhibit PCSK9 demonstrates the utility of translating genetics into clinical therapeutics. Attempts to identify genes responsible for hypercholesterolaemia have used traditional linkage analysis, which requires samples collected from multiple families with defects in the same gene, or genome-wide association, which requires thousands of samples from the population. More recently, whole-exome sequencing studies have revealed loss-of-function mutations in ANGPTL3 associated with pan-hypolipidemia, and in APOC3 that confer protection against CHD. The application of whole-exome sequencing to large populations or to carefully selected patients can streamline the discovery of causal genetic mutations.

Genetics of coronary artery disease and myocardial infarction

Atherosclerotic coronary artery disease (CAD) comprises a broad spectrum of clinical entities that include asymptomatic subclinical atherosclerosis and its clinical complications, such as angina pectoris, myocardial infarction (MI) and sudden cardiac death. CAD continues to be the leading cause of death in industrialized society. The long-recognized familial clustering of CAD suggests that genetics plays a central role in its development, with the heritability of CAD and MI estimated at approximately 50% to 60%. Understanding the genetic architecture of CAD and MI has proven to be difficult and costly due to the heterogeneity of clinical CAD and the underlying multi-decade complex pathophysiological processes that involve both genetic and environmental interactions. This review describes the clinical heterogeneity of CAD and MI to clarify the disease spectrum in genetic studies, provides a brief overview of the historical understanding and estimation of the heritability of CAD and MI, recounts major gene discoveries of potential causal mutations in familial CAD and MI, summarizes CAD and MI-associated genetic variants identified using candidate gene approaches and genome-wide association studies (GWAS), and summarizes the current status of the construction and validations of genetic risk scores for lifetime risk prediction and guidance for preventive strategies. Potential protective genetic factors against the development of CAD and MI are also discussed. Finally, GWAS have identified multiple genetic factors associated with an increased risk of in-stent restenosis following stent placement for obstructive CAD. This review will also address genetic factors associated with in-stent restenosis, which may ultimately guide clinical decision-making regarding revascularization strategies for patients with CAD and MI.

Next-generation-sequencing-based identification of familial hypercholesterolemia-related mutations in subjects with increased LDL-C levels in a latvian population

BACKGROUND

Familial hypercholesterolemia (FH) is one of the commonest monogenic disorders, predominantly inherited as an autosomal dominant trait. When untreated, it results in early coronary heart disease. The vast majority of FH remains undiagnosed in Latvia. The identification and early treatment of affected individuals remain a challenge worldwide. Most cases of FH are caused by mutations in one of four genes, APOB, LDLR, PCSK9, or LDLRAP1. The spectrum of disease-causing variants is very diverse and the variation detection panels usually used in its diagnosis cover only a minority of the disease-causing gene variants. However, DNA-based tests may provide an FH diagnosis for FH patients with no physical symptoms and with no known family history of the disease. Here, we evaluate the use of targeted next-generation sequencing (NGS) to identify cases of FH in a cohort of patients with coronary artery disease (CAD) and individuals with abnormal low-density lipoprotein-cholesterol (LDL-C) levels.

METHODS

We used targeted amplification of the coding regions of LDLR, APOB, PCSK9, and LDLRAP1, followed by NGS, in 42 CAD patients (LDL-C, 4.1-7.2 mmol/L) and 50 individuals from a population-based cohort (LDL-C, 5.1-9.7 mmol/L).

RESULTS

In total, 22 synonymous and 31 nonsynonymous variants, eight variants in close proximity (10 bp) to intron-exon boundaries, and 50 other variants were found. We identified four pathogenic mutations (p.(Arg3527Gln) in APOB, and p.(Gly20Arg), p.(Arg350*), and c.1706-10G > A in LDLR) in seven patients (7.6 %). Three possible pathogenic variants were also found in four patients.

CONCLUSION

NGS-based methods can be used to detect FH in high-risk individuals when they do not meet the defined clinical criteria.

The history of Autosomal Recessive Hypercholesterolemia (ARH). From clinical observations to gene identification

The most frequent form of monogenic hypercholesterolemia, also known as Familial Hypercholesterolemia (FH), is characterized by plasma accumulation of cholesterol transported in Low Density Lipoproteins (LDLs). FH has a co-dominant transmission with a gene-dosage effect. FH heterozygotes have levels of plasma LDL-cholesterol (LDL-C) twice normal and present xanthomas and coronary heart disease (CHD) in adulthood. In rare FH homozygotes plasma LDL-C level is four times normal, while xanthomas and CHD are present from infancy. Most FH patients are carriers of mutations of the LDL receptor (LDLR); a minority of them carry either mutations in the Apolipoprotein B (ApoB), the protein constituent of LDLs which is the ligand for LDLR, or gain of function mutations of PCSK9, the protein responsible for the intracellular degradation of the LDLR. From 1970 to the mid 90s some publications described children with the clinical features of homozygous FH, who were born from normocholesterolemic parents, strongly suggesting a recessive transmission of FH. In these patients the involvement of LDLR and APOB genes was excluded. Interestingly, several patients were identified in the island of Sardinia (Italy), whose population has a peculiar genetic background due to geographical isolation. In this review, starting from the early descriptions of patients with putative recessive hypercholesterolemia, we highlight the milestones that led to the identification of a novel gene involved in LDL metabolism and the characterization of its encoded protein. The latter turned out to be an adaptor protein required for the LDLR-mediated endocytosis of LDLs in hepatocytes. The loss of function of this protein is the cause of Autosomal Recessive Hypercholesterolemia (ARH).

Pharmacological treatment of a Sardinian patient affected by Autosomal Recessive Hypercholesterolemia (ARH)

BACKGROUND AND AIM

Previous studies have shown that patients with autosomal recessive hypercholesterolemia (ARH) resulting from mutations in LDLRAP1 gene have a less severe cardiovascular involvement than familial hypercholesterolemia homozygotes, lower levels of low-density lipoprotein cholesterol (LDL-C), and higher levels of high-density lipoprotein cholesterol (HDL-C). In addition, ARH patients seem to be more responsive to the lipid-lowering drugs. The aim was to test the effect of a combined drug treatment in an ARH patient in the absence of plasmapheresis.

METHODS AND RESULTS

Here we report the lipid-lowering effect of rosuvastatin (60 mg/day) associated with ezetimibe (10 mg/day) in a single ARH patient. The sequencing of LDLRAP1 gene showed that the patient was homozygous for the c.432insA mutation. During a 6-month treatment, we observed an 80% reduction of LDL-C and a significant increase of HDL-C and ApoA-I. Some sequence variations in PCSK9 and NPC1L1 genes found in this patient may have contributed to the success of drug treatment.

CONCLUSIONS

Our findings, although limited to a single case, suggest that in many ARH patients the LDL-C goal may be reached with the more potent statins associated with ezetimibe in the absence of extracorporeal procedures.

Autosomal recessive hypercholesterolemia: a mild phenotype of familial hypercholesterolemia: insight from the kinetic study using stable isotope and animal studies

Autosomal recessive hypercholesterolemia (ARH) is an extremely rare inherited disorder, the cause of which is mutations in the low-density lipoprotein (LDL) receptor adaptor protein 1 (LDLRAP1) gene. Only 36 families with 14 different mutations have been reported in the literature to date. The clinical phenotype of ARH is milder than that of homozygous familial hypercholesterolemia (FH) caused by LDL receptor gene mutations. Recently, the lipoprotein metabolism of ARH was investigated in both humans and mice by several investigators, including ourselves. Based on these findings the preserved clearance of LDL receptor-dependent very-LDL (VLDL) may be a possible mechanism underlying the responsiveness to statins and the milder phenotype of ARH. Although ARH has been described as being "recessive," several studies, including ours, have indicated that a heterozygous carrier status of the LDLRAP1 gene is associated with mild hypercholesterolemia and exacerbates the phenotype of FH resulting from LDL receptor gene mutations. This review summarizes current understanding regarding ARH and its causative gene, LDLRAP1, and attempts to provide new insight into novel pharmacological targets for treating dyslipidemic patients.

Microsomal transfer protein (MTP) inhibition-a novel approach to the treatment of homozygous hypercholesterolemia

Homozygous familial hypercholesterolemia (HoFH) represents the most severe lipoprotein disorder, generally attributable to mutation(s) of the low-density lipoprotein receptor (LDL-R), i.e. autosomal dominant hypercholesterolemia type 1 (ADH1). Much lower percentages are due to alterations of apolipoprotein B (ADH2), or gain-of-function mutations of proprotein convertase subtilisin/kexin type 9 (PCSK9) (ADH3). In certain geographical areas a significant number of patients may be affected by an autosomal recessive hypercholesterolemia (ARH). Mutations may be also combined (two mutations of the same gene, compound heterozygosity), or two in different genes (double heterozygosity). Among the most innovative therapeutic approaches made available recently, inhibitors of the microsomal transfer protein (MTP) system have shown a high clinical potential. MTP plays a critical role in the assembly/secretion of very-low-density lipoproteins (VLDL), and its absence leads to apo B deficiency. MTP antagonists dramatically lower LDL-cholesterol (LDL-C) in animals, although a reported increase of liver fat delayed their clinical development. Lomitapide, the best-studied MTP inhibitor, reduces LDL-C by 50% or more in HoFH patients, with modest, reversible, liver steatosis. Recent US approval has confirmed an acceptable tolerability, provided patients adhere to a strictly low-fat regimen. There are no clinical data on atherosclerosis reduction/regression, but animal models provide encouraging results.

Familial hypercholesterolemia: A review

Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism resulting in elevated serum low-density lipoprotein (LDL) cholesterol levels leading to increased risk for premature cardiovascular diseases (CVDs). The diagnosis of this condition is based on clinical features, family history, and elevated LDL-cholesterol levels aided more recently by genetic testing. As the atherosclerotic burden is dependent on the degree and duration of exposure to raised LDL-cholesterol levels, early diagnosis and initiation of treatment is paramount. Statins are presently the mainstay in the management of these patients, although newer drugs, LDL apheresis, and other investigational therapies may play a role in certain subsets of FH, which are challenging to treat. Together these novel treatments have notably improved the prognosis of FH, especially that of the heterozygous patients. Despite these achievements, a majority of children fail to attain targeted lipid goals owing to persistent shortcomings in diagnosis, monitoring, and treatment. This review aims to highlight the screening, diagnosis, goals of therapy, and management options in patients with FH.

The LRP6 rs2302685 polymorphism is associated with increased risk of myocardial infarction

Background

Abnormal lipids is one of the critical risk factors for myocardial infarction (MI), however the role of genetic variants in lipid metabolism-related genes on MI pathogenesis still requires further investigation. We herein genotyped three SNPs (LRP6 rs2302685, LDLRAP1 rs6687605, SOAT1 rs13306731) in lipid metabolism-related genes, aimed to shed light on the influence of these SNPs on individual susceptibility to MI.

Methods

Genotyping of the three SNPs (rs2302685, rs6687605 and rs13306731) was performed in 285 MI cases and 650 control subjects using polymerase chain reaction–ligation detection reaction (PCR–LDR) method. The association of these SNPs with MI and lipid profiles was performed with SPSS software.

Results

Multivariate logistic regression analysis showed that C allele (OR = 1.62, P = 0.039) and the combined CT/CC genotype (OR = 1.67, P = 0.035) of LRP6 rs2302685 were associated with increased MI risk, while the other two SNPs had no significant effect. Further stratified analysis uncovered a more evident association with MI risk among younger subjects (≤60 years old). Fascinatingly, CT/CC genotype of rs2302685 conferred increased LDL-C levels compared to TT genotype (3.0 mmol/L vs 2.72 mmol/L) in younger subjects.

Conclusions

Our data provides the first evidence that LRP6 rs2302685 polymorphism is associated with an increased risk of MI in Chinese subjects, and the association is more evident among younger individuals, which probably due to the elevated LDL-C levels.

Diagnosis and management of familial dyslipoproteinemias

The three major pathways of lipoprotein metabolism provide a superb paradigm to delineate systematically the familial dyslipoproteinemias. Such understanding leads to improved diagnosis and treatment of patients. In the exogenous (intestinal) pathway, defects in LPL, apoC-II, APOA-V, and GPIHBP1 disrupt the catabolism of chylomicrons and hepatic uptake of their remnants, producing very high TG. In the endogenous (hepatic) pathway, six disorders affect the activity of the LDLR and markedly increase LDL. These include FH, FDB, ARH, PCSK9 gain-of-function mutations, sitosterolemia and loss of 7 alpha hydroxylase. Hepatic overproduction of VLDL occurs in FCHL, hyperapoB, LDL subclass pattern B, FDH and syndrome X, often due to insulin resistance and resulting in high TG, elevated small LDL particles and low HDL-C. Defects in APOB-100 and loss-of-function mutations in PCSK9 are associated with low LDL-C, decreased CVD and longevity. An absence of MTP leads to marked reduction in chylomicrons and VLDL, causing abetalipoproteinemia. In the reverse cholesterol pathway, deletions or nonsense mutations in apoA-I or ABCA1 transporter disrupt the formation of the nascent HDL particle. Mutations in LCAT disrupt esterification of cholesterol in nascent HDL by LCAT and apoA-1, and formation of spherical HDL. Mutations in either CETP or SR-B1 and familial high HDL lead to increased large HDL particles, the effect of which on CVD is not resolved. The major goal is to prevent or ameliorate the major complications of many familial dyslipoproteinemias, namely, premature CVD or pancreatitis. Dietary and drug treatment specific for each inherited disorder is reviewed.

Lysosomal acid lipase A and the hypercholesterolaemic phenotype

PURPOSE OF REVIEW

Mutations in lysosomal acid lipase A (LIPA) result in two phenotypes depending on the extent of lysosomal acid lipase (LAL) deficiency: the severe, early-onset Wolman disease or the less severe cholesteryl ester storage disease (CESD). In CESD, the severity of the symptoms, hepatomegaly and hypercholesterolaemia, can be highly variable, presenting in childhood or adulthood. Therefore, it is likely that many patients are undiagnosed or misdiagnosed. Nevertheless, LAL deficiency has been recognized for more than 25 years, but adequate therapeutic strategies are limited.

RECENT FINDINGS

CESD has an estimated prevalence of one in 90,000 to 170,000 individuals in the general population, confirming the likelihood that this disease is currently underdiagnosed. A number of studies have shown that in LIPA deficient patients the hypercholesterolaemic phenotype can be attenuated using statin therapy, and favourable effects on reduction of lipid accumulation in lysosomes have been reported. Targeting lysosomal exocytosis with LAL replacement therapy was shown to be successful in animal models and recently a phase I/II study demonstrated its safety and its potential metabolic efficacy on transaminase levels.

SUMMARY

The hypercholesterolaemic phenotype in CESD can be difficult to distinguish from other known hypercholesterolaemic disorders. In the majority of CESD cases with hypercholesterolaemia favourable responses on statin treatment are observed, but the effect on reduction of lipid accumulation in lysosomes needs to be further evaluated. Combining statins with LAL replacement therapy may provide a promising approach for optimal treatment of LIPA deficiencies in the future.

S-nitrosylation of ARH is required for LDL uptake by the LDL receptor

The LDL receptor (LDLR) relies upon endocytic adaptor proteins for internalization of lipoproteins. The results of this study show that the LDLR adaptor autosomal recessive hypercholesterolemia protein (ARH) requires nitric oxide to support LDL uptake. Nitric oxide nitrosylates ARH at C199 and C286, and these posttranslational modifications are necessary for association of ARH with the adaptor protein 2 (AP-2) component of clathrin-coated pits. In the absence of nitrosylation, ARH is unable to target LDL-LDLR complexes to coated pits, resulting in poor LDL uptake. The role of nitric oxide on LDLR function is specific for ARH because inhibition of nitric oxide synthase activity impairs ARH-supported LDL uptake but has no effect on other LDLR-dependent lipoprotein uptake processes, including VLDL remnant uptake and dab2-supported LDL uptake. These findings suggest that cells that depend upon ARH for LDL uptake can control which lipoproteins are internalized by their LDLRs through changes in nitric oxide.

Endocytosis and signaling: cell logistics shape the eukaryotic cell plan

Our understanding of endocytosis has evolved remarkably in little more than a decade. This is the result not only of advances in our knowledge of its molecular and biological workings, but also of a true paradigm shift in our understanding of what really constitutes endocytosis and of its role in homeostasis. Although endocytosis was initially discovered and studied as a relatively simple process to transport molecules across the plasma membrane, it was subsequently found to be inextricably linked with almost all aspects of cellular signaling. This led to the notion that endocytosis is actually the master organizer of cellular signaling, providing the cell with understandable messages that have been resolved in space and time. In essence, endocytosis provides the communications and supply routes (the logistics) of the cell. Although this may seem revolutionary, it is still likely to be only a small part of the entire story. A wealth of new evidence is uncovering the surprisingly pervasive nature of endocytosis in essentially all aspects of cellular regulation. In addition, many newly discovered functions of endocytic proteins are not immediately interpretable within the classical view of endocytosis. A possible framework, to rationalize all this new knowledge, requires us to "upgrade" our vision of endocytosis. By combining the analysis of biochemical, biological, and evolutionary evidence, we propose herein that endocytosis constitutes one of the major enabling conditions that in the history of life permitted the development of a higher level of organization, leading to the actuation of the eukaryotic cell plan.