The type of LDLR gene mutation predicts cardiovascular risk in children with familial hypercholesterolemia

Novel LDLR variants affecting low density lipoprotein metabolism identified in familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is an autosomal dominant disease of lipid metabolism mainly caused by mutations in the low-density lipoprotein receptor (LDLR) gene. Genetic detection of patients with FH help with precise diagnosis and treatment, thus reducing the risk of coronary heart disease (CHD) and other related diseases. The study aimed to identify the causative gene mutations in a Chinese FH family and reveal the pathogenicity and the mechanism of these mutations.

METHODS AND RESULTS

Whole exome sequencing was performed in a patient with severe lipid metabolism dysfunction seeking fertility guidance from a Chinese FH family. Two LDLR variants c.1875 C > G (p.N625K; novel variant) and c.1448G > A (p.W483*) were identified in the family. Wildtype and mutant LDLR constructs were established by the site-direct mutagenesis technique. Functional studies were carried out by cell transfection to evaluate the impact of detected variants on LDLR activity. The two variants were proven to affect LDL uptake and binding, resulting in cholesterol clearance reduction to different degrees. According to The American College of Medical Genetics and Genomics (ACMG) Standards and Guidelines, the W483* variant was classified as "Pathogenic", while the N625K variant as "VUS".

CONCLUSIONS

Our results provide novel experimental evidence of functional alteration by LDLR variants identified in our study and expand the mutational spectrum of LDLR mutation induced FH.

Genotype-phenotype correlation in a large cohort of pediatric patients with heterozygous and homozygous familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is a genetic disorder characterized by elevated low-density lipoprotein cholesterol (LDL-C) levels and premature cardiovascular disease (CVD). Both the heterozygous form and the very severe homozygous form can be diagnosed by genetic testing and by clinical criteria. Genetic testing can discern FH in a form caused by complete absence of the LDL-receptors, the negative variant and a form leading to reduced activity of the LDL receptors, the defective variant. The aim of this study is to provide more insight in the genotype-phenotype correlation in children and adolescents diagnosed with heterozygous FH (HeFH) and with homozygous FH (HoFH), specifically in relation to the clinical and therapeutic consequences of the negative and defective variant of FH.

METHODS AND RESULTS

Data of 5904 children with a tentative diagnosis of FH referred to our center for genetic testing were collected. A lipid-profile was present in 3494 children, who became the study cohort. In this large cohort of children, which includes 2714 HeFH and 41 HoFH patients, it is shown that receptor negative variants are associated with significant higher LDL-C levels in HeFH patients than receptor defective variants (6.0 versus 4.9 mmol/L; p  < 0.001). A negative/negative variant is associated with a significant higher LDL-C level jn HoFH patients than a negative/defective variant, which in itself has a higher LDL-C level than a defective/defective variant. Significantly more premature CVD is present in close relatives of children with HeFH with negative variants compared to close relatives of HeFH children with defective variants (75% vs 59%; p  < 0.001).

CONCLUSIONS

Performing genetic testing and identifying the type of underlying genetic variant is of added value in order to distinguish between pediatric patients with higher risks of premature CVD and to identify those that will benefit most from new types of lipid-lowering therapies. Since in children the phenotype of FH is less affected by environmental factors, the study substantiates the genotype-phenotype correlation in this large pediatric population.

Effect of the LDL receptor mutation type on incident major adverse cardiovascular events in familial hypercholesterolaemia

AIMS

Patients with familial hypercholesterolaemia (FH) are at increased risk of cardiovascular disease (CVD) due to extremely high circulating LDL cholesterol (LDL-C) concentrations. Our objective was to study the effect of the type of LDL receptor (LDLR) mutation on the incidence of major adverse cardiovascular events (MACEs).

METHODS AND RESULTS

This was a multinational prospective cohort study, which included patients with heterozygous FH aged 18-65 years, without a prior history of CVD, and carrying a pathogenic or likely pathogenic variant in the LDLR gene. A total of 2131 patients (20 535person-years of follow-up) were included in the study, including 1234 subjects carrying a defective mutation in the LDLR and 897 subjects carrying a null mutation. During the follow-up, a first MACE occurred in 79 cases (6%) in the defective group and in 111 cases (12%) in the null group. The mean baseline LDL-C concentration was 17% higher in the null group than in the defective group (7.90 vs. 6.73 mmoL/L, P < 0.0001). In a Cox regression model corrected for traditional cardiovascular risk factors, the presence of a null mutation was associated with a hazard ratio of 2.09 (1.44-3.05), P = 0.0001.

CONCLUSION

Carriers of a null mutation have an independent ∼2-fold increased risk of incident MACE compared with patients carrying a defective mutation. This study highlights the importance of genetic screening in FH in order to improve patient care.

Risk Assessment and Clinical Management of Children and Adolescents with Heterozygous Familial Hypercholesterolaemia. A Position Paper of the Associations of Preventive Pediatrics of Serbia, Mighty Medic and International Lipid Expert Panel

Heterozygous familial hypercholesterolaemia (FH) is among the most common genetic metabolic lipid disorders characterised by elevated low-density lipoprotein cholesterol (LDL-C) levels from birth and a significantly higher risk of developing premature atherosclerotic cardiovascular disease. The majority of the current pediatric guidelines for clinical management of children and adolescents with FH does not consider the impact of genetic variations as well as characteristics of vascular phenotype as assessed by recently developed non-invasive imaging techniques. We propose a combined integrated approach of cardiovascular (CV) risk assessment and clinical management of children with FH incorporating current risk assessment profile (LDL-C levels, traditional CV risk factors and familial history) with genetic and non-invasive vascular phenotyping. Based on the existing data on vascular phenotype status, this panel recommends that all children with FH and cIMT ≥0.5 mm should receive lipid lowering therapy irrespective of the presence of CV risk factors, family history and/or LDL-C levels Those children with FH and cIMT ≥0.4 mm should be carefully monitored to initiate lipid lowering management in the most suitable time. Likewise, all genetically confirmed children with FH and LDL-C levels ≥4.1 mmol/L (160 mg/dL), should be treated with lifestyle changes and LLT irrespective of the cIMT, presence of additional RF or family history of CHD.

Familial Hypercholesterolemia Genetic Variations and Long-Term Cardiovascular Outcomes in Patients with Hypercholesterolemia Who Underwent Coronary Angiography

Background: Familial hypercholesterolemia (FH) has been associated with early coronary artery disease (CAD) and increased risk of atherosclerotic cardiovascular disease. However, the prevalence of FH and its long-term outcomes in a CAD-high-risk cohort, defined as patients with hypercholesteremia who underwent coronary angiography, remains unknown. Besides, studies regarding the impact of genetic variations in FH on long-term cardiovascular (CV) outcomes are scarce. Methods and Results: In total, 285 patients hospitalized for coronary angiography with blood low-density lipoprotein cholesterol (LDL-C) levels ≥ 160 mg/dL were sequenced to detect FH genetic variations in LDL receptors apolipoprotein B and proprotein convertase subtilisin/kexin type 9. Risk factors associated with long-term CV outcomes were evaluated. The prevalence of FH was high (14.4%). CAD and early CAD were significantly more prevalent among FH variation carriers than non-carriers, despite comparable blood LDL-C levels. Moreover, the FH variation carriers also underwent more revascularization after a mean follow-up of 6.1 years. Multivariate logistic regression demonstrated that FH genetic variation was associated with increased incidence of cardiovascular disease and mortality (odds ratio = 3.17, p = 0.047). Two common FH variants, LDLR c.986G>A and LDLR c.268G>A, showed the most significant impacts on high blood LDL-C levels and early-onset CAD. Conclusions: Our results indicate that FH genetic variants may exhibit differential effects on early-onset CAD and revascularization risks in patients undergoing coronary angiography. FH genetic information might help identify high-risk patients with typical CAD symptoms for appropriate intervention.

Early Prevention of Atherosclerosis: Detection and Management of Hypercholesterolaemia in Children and Adolescents

Coronary heart disease (CHD) is the main cause of death and morbidity in the world. There is a strong evidence that the atherosclerotic process begins in childhood and that hypercholesterolaemia is a CHD major risk factor. Hypercholesterolaemia is a modifiable CHD risk factor and there is a tracking of hypercholesterolaemia from birth to adulthood. Familial hypercholesterolaemia (FH) is the most common primitive cause of hypercholesterolaemia, affecting 1:200–250 individuals. Early detection and treatment of hypercholesterolaemia in childhood can literally “save decades of life”, as stated in the European Atherosclerosis Society Consensus. Multiple screening strategies have been proposed. In 2008, the American Academy of Pediatrics published the criteria for targeted screening, while some expert panels recommend universal screening particularly in the young, although cost effectiveness has not been fully analysed. Blood lipid profile evaluation [total cholesterol, Low-Density Lipoprotein Cholesterol (LDL-C), High-Density Lipoprotein Cholesterol (HDL-C) and triglycerides] is the first step. It has to be ideally performed between two and ten years of age. Hypercholesterolaemia has to be confirmed with a second sample and followed by the detection of family history for premature (before 55 years in men and 60 years in women) or subsequent cardio-vascular events and/or hypercholesterolaemia in 1st and 2nd degree relatives. The management of hypercholesterolaemia in childhood primarily involves healthy lifestyle and a prudent low-fat diet, emphasising the benefits of the Mediterranean diet. Statins are the cornerstone of the drug therapy approved in USA and in Europe for use in children. Ezetimibe or bile acid sequestrants may be required to attain LDL-C goal in some patients. Early identification of children with severe hypercholesterolaemia or with FH is important to prevent atherosclerosis at the earliest stage of development, when maximum benefit can still be obtained via lifestyle adaptations and therapy. The purpose of our review is to highlight the importance of prevention and treatment of hypercholesterolaemia starting from the earliest stages of life.

The Spectrum of Low-Density Lipoprotein Receptor Mutations in a Large Turkish Cohort of Patients with Familial Hypercholesterolemia

Background: Monogenic hypercholesterolemia with Mendelian inheritance is a heterogeneous group of diseases that are characterized by elevated plasma low-density lipoprotein cholesterol (LDL-C) levels, and the most common form of this disorder is autosomal-dominant familial hypercholesterolemia (FH). Methods: A total of 104 index cases with the clinical diagnosis of FH were included in this study. Low-density lipoprotein receptor (LDLR) was sequenced using the Sanger sequencing method. Results: Pathogenic/likely pathogenic variants were detected in LDLR in 55 of the 104 cases (mutation detection rate = 52.8%). Thirty different variants were detected in LDLR, three of which were novel. The total cholesterol and LDL-C values of the patients in the group of premature termination codon (PTC) mutation carriers were significantly higher than those of the patients in the group of non-PTC mutation carriers. A total of 87 patients (17 pediatric and 70 adult cases) were diagnosed with cascade genetic screening. Statin treatment was recommended to all 87 patients and was accepted and initiated in 70 of these patients. Conclusions: This study is the largest patient cohort that evaluated FH cases in the Turkish population. Herein, we revealed the LDLR mutation spectrum for a Turkish population and compared the cases in the context of genotype-phenotype correlation. Genetic screening of individuals with suspected FH not only helps to establish their diagnosis, but also facilitates early diagnosis and treatment initiation in other family members through cascade screening.

The Digenic Causality in Familial Hypercholesterolemia: Revising the Genotype-Phenotype Correlations of the Disease

Genetically inherited defects in lipoprotein metabolism affect more than 10 million individuals around the globe with preponderance in some parts where consanguinity played a major role in establishing founder mutations. Mutations in four genes have been so far linked to the dominant and recessive form of the disease. Those players encode major proteins implicated in cholesterol regulation, namely, the low-density lipoprotein receptor (LDLR) and its associate protein 1 (LDLRAP1), the proprotein convertase substilin/kexin type 9 (PCSK9), and the apolipoprotein B (APOB). Single mutations or compound mutations in one of these genes are enough to account for a spectrum of mild to severe phenotypes. However, recently several reports have identified digenic mutations in familial cases that do not necessarily reflect a much severe phenotype. Yet, data in the literature supporting this notion are still lacking. Herein, we review all the reported cases of digenic mutations focusing on the biological impact of gene dosage and the potential protective effects of single-nucleotide polymorphisms linked to hypolipidemia. We also highlight the difficulty of establishing phenotype-genotype correlations in digenic familial hypercholesterolemia cases due to the complexity and heterogeneity of the phenotypes and the still faulty in silico pathogenicity scoring system. We finally emphasize the importance of having a whole exome/genome sequencing approach for all familial cases of familial hyperlipidemia to better understand the genetic and clinical course of the disease.

The Effect of Long-Term Atorvastatin Therapy on Carotid Intima-Media Thickness of Children With Dyslipidemia

Carotid intima-media thickness (cIMT) has been proposed as an early marker of subclinical atherosclerosis in high risk children. Children with heterozygous familial hypercholesterolemia have greater cIMT than matched healthy controls or their unaffected siblings. Statin therapy may delay the progression of cIMT, although long-term studies in children are scarce. We evaluated the effect of atorvastatin treatment on cIMT in children with dyslipidemia. We studied 81 children/adolescents, 27 with severe dyslipidemia (low-density lipoprotein cholesterol [LDL-C] ≥190 mg/dL) and 54 sex- and age-matched healthy controls; LDL-C ≤ 130 mg/dL and lipoprotein (a), Lp(a), ≤30 mg/dL. In the children with dyslipidemia, cIMT was measured twice, before and on treatment (18.2 ± 7.7 months). Anthropometric data, a full lipid profile, liver, kidney, and thyroid function were evaluated. Males with dyslipidemia had a greater cIMT than male controls after adjustment for other factors (P = .049). In addition, a nonstatistically significant decrease in cIMT was observed after treatment (P = .261). Treatment with atorvastatin resulted in a significantly improved lipid profile. Females with dyslipidemia had a significantly thinner cIMT than males. Children with normal and high Lp(a) levels had similar cIMT values. In conclusion, treatment with atorvastatin had a beneficial effect on the lipid profile and cIMT progression in children with severe dyslipidemia.

Long term follow-up of genetically confirmed patients with familial hypercholesterolemia treated with first and second-generation statins and then with PCSK9 monoclonal antibodies

BACKGROUND AND AIMS

In Italy, the clinical and genetic characteristics of familial hypercholesterolemia (FH) have been extensively assessed in various lipid clinics, although no studies on long-term cardiovascular outcomes in heterozygous patients (He-FH) have been conducted. This study evaluated the incidence of atherosclerotic cardiovascular disease (ASCVD) in He-FH before and after a long-term period of lipid-lowering treatments to ascertain the interference of other risk factors.

METHODS

A total of 294 genetically characterised He-FH subjects from 1989 to 2019 were retrospectively analysed. General characteristics, lipid profiles, ASCVD prevalence, and ultrasound carotid atherosclerosis assessment were evaluated. Primary end points were ASCVD outcomes and the percentage of patients reaching recommended LDL-C targets.

RESULTS

During follow-up, despite a significant improvement in plasma lipid profiles, the ESC/EAS 2016 and 2019 recommended LDL cholesterol (LDL-C) goals were attained in only a few patients treated with anti-PCSK9 monoclonal antibodies added to the maximum tolerated oral therapy with statins plus ezetimibe. Forty-seven subjects had an ASCVD event before starting lipid-lowering therapy (LLT). During follow-up (median 13 years) on LLT, 28 patients had a first ASCVD event and 16 had recurrent ASCVD. In basal conditions and during follow-up, higher LDL-C levels were associated with increased ASCVD risk (p < 0.001). Prevention of recurrent ASCVD events was recorded with a long-term reduction of LDL-C below 100 mg/dl with statins plus ezetimibe.

CONCLUSIONS

PCSK9 inhibition is the only therapeutic option to achieve LDL-C goals as recommended for He-FH and can prevent ASCVD events as reported in large clinical trials. Long-term treatment with statins and ezetimibe seems to be effective at preventing ASCVD recurrence when LDL-C is maintained below 130 and 100 mg/dL for primary and secondary prevention, respectively.

"Apple does not fall far from the tree" - subclinical atherosclerosis in children with familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) increases the risk of atherosclerosis in children and adults. Atherosclerotic cardiovascular disease in young patients FH is usually subclinical but recognition of children with more pronounced changes is crucial for adjusting effective management. Aim of this research was to use ultrasonography with two-dimensional speckle tracking (2DST) and tonometry to evaluate atherosclerotic changes in patients with FH (parents and their offspring).

METHODS

Applanation tonometry and carotid arteries sonography with evaluation of the intima-media complex thickness (IMCT) and application of the 2DST were performed in 20 families with FH (20 parents and 29 children). The same size control group (age and sex matched) was included. Results were compared between peers and between generations together with the correlation analysis.

RESULTS

Adults with FH, in comparison with healthy peers, presented significantly more atherosclerotic plaques (9 vs. 2, p = 0.0230), had significantly thicker IMC (0.84 ± 0.19 vs. 0.56 ± 0.06 mm, p < 0.0001) and had stiffer arterial wall (for stain: 6.25 ± 2.3 vs. 8.15 ± 2.46, p = 0.0103). In children from both groups there were no atherosclerotic plaques and IMCT did not differ significantly (0.42 ± 0.07 vs. 0.39 ± 0.04, p = 0.1722). However, children with FH had significantly stiffer arterial wall according to 2DST (for strain: 9.22 ± 3.4 vs. 11.93 ± 3.11, p = 0.0057) and tonometry (for the pulse wave velocity: 4.5 ± 0.64 vs.3.96 ± 0.62, p = 0.0047). These parameters correlated with atherosclerosis surrogates in their parents (p < 0.001) but were not significantly affected by presence of presumed pathogenic gene variant.

CONCLUSIONS

Children with FH presented subclinical atherosclerosis manifested as decreased arterial wall elasticity. Degree of stiffening was associated with advancement of atherosclerosis in their parents but did not present significant association with gene variants. Sonography with application of 2DST seems to be a good candidate for comprehensive evaluation of atherosclerosis in families with FH.

Why patients with familial hypercholesterolemia are at high cardiovascular risk? Beyond LDL-C levels

Familial hypercholesterolemia (FH) is a common genetic cause of elevated low-density lipoprotein cholesterol (LDL-C) due to defective clearance of circulating LDL particles. All FH patients are at high risk for premature cardiovascular disease (CVD) events due to their genetically determined lifelong exposure to high LDL-C levels. However, different rates of CVD events have been reported in FH patients, even among those with the same genetic mutations and comparable LDL-C levels. Hence, additional CVD risk modifiers, beyond LDL-C, may contribute to increase CVD risk in the FH population. In this review, we discuss the overall CVD risk burden of the FH population. Additionally, we revise the prognostic impact of several traditional and emerging predictors of CVD risk and we provide an overview of the role of specific tools to stratify CVD risk in FH patients in order to ensure them a more personalized treatment approach.

p.(Asp47Asn) and p.(Thr62Met): non deleterious LDL receptor missense variants functionally characterized in vitro

Familial Hypercholesterolemia (FH) is a common genetic disorder caused most often by mutations in the Low Density Lipoprotein Receptor gene (LDLr) leading to high blood cholesterol levels, and ultimately to development of premature coronary heart disease. Genetic analysis and subsequent cascade screening in relatives allow diagnosis of FH at early stage, especially relevant to diagnose children. So far, more than 2300 LDLr variants have been described but only a minority of them have been functionally analysed to evaluate their pathogenicity in FH. Thus, identifying pathogenic mutations in LDLr is a long-standing challenge in the field. In this study, we investigated in vitro the activity p.(Asp47Asn) and p.(Thr62Met) LDLr variants, both in the LR1 region. We used CHO-ldlA7 transfected cells with plasmids carrying p.(Asp47Asn) or p.(Thr62Met) LDLr variants to analyse LDLr expression by FACS and immunoblotting, LDL binding and uptake was determined by FACS and analysis of mutation effects was assessed in silico. The in vitro activity assessment of p.(Asp47Asn) and p.(Thr62Met) LDLr variants shows a fully functional LDL binding and uptake activities. Therefore indicating that the three of them are non-pathogenic LDLr variants. These findings also emphasize the importance of in vitro functional LDLr activity studies to optimize the genetic diagnosis of FH avoiding the report of non-pathogenic variants and possible misdiagnose in relatives if cascade screening is carried out.

Spectrum of mutations of familial hypercholesterolemia in the 22 Arab countries

BACKGROUND AND AIMS

Familial hypercholesterolemia (FH) is an inherited genetic disorder of lipid metabolism characterized by a high serum LDL-cholesterol profile and xanthoma formation, and FH increases the risk of premature atherosclerosis and cardiovascular disease (CVD). Mutations in the low-density lipoprotein (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin 9 (PCSK9), and LDLRAP1 genes have been associated with FH. Although FH is a major risk for CVD, the disease prevalence and its underlying molecular basis in the 22 Arab countries are still understudied. This study aimed to analyze all peer-reviewed studies related to the prevalence of FH and its causative mutations in the 22 Arab countries.

METHODS

We searched five literature databases (Scopus, Science Direct, Web of Science, PubMed, and Google Scholar) from inception until June 2018, using all possible search terms to capture all of the genetic and prevalence data related to Arab patients with FH.

RESULTS

A total of 5,484 titles and abstracts were identified; 51 studies met our inclusion criteria for the final systematic review. Fifty-one mutations in Arab patients with FH were identified in only eight Arab countries; 47 were identified in the LDLR gene, two in the PCSK9 gene, and two in LDLRAP1 gene. Twenty mutations in the LDLR gene were distinctive to Arab patients. A few studies reported prevalence estimates, ranging from 0.4% to 6.8%.

CONCLUSIONS

This is the first systematic review to dissect the up-to-date status of the genetic epidemiology of Arab patients with FH. It seems that FH is underdiagnosed and that its prevalence is understudied due to the dearth of published information about Arab patients with FH. Therefore, there is a need for well-controlled genetic epidemiological studies on Arab patients with FH.

Screening of LDLR and APOB gene mutations in Mexican patients with homozygous familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is an autosomal dominant disorder that causes accumulation of serum low-density lipoprotein cholesterol and premature cardiovascular disease. It is mainly related to mutations in the LDLR gene. Homozygous FH (HoFH) patients have the most severe form of the disease accounting for a worldwide prevalence of 1:1,000,000. In Mexico, at least 5 cases of HoFH have been reported.

OBJECTIVE

The aim of this study was to describe the clinical, biochemical, and molecular data observed in patients with HoFH phenotype.

METHODS

We included 13 patients, belonging to 11 families, with clinical and biochemical diagnoses suggestive of HoFH. Molecular analyses of the LDLR and APOB genes were performed by means of polymerase chain reaction followed by Sanger sequencing.

RESULTS

The causal mutation of HoFH was found in 8 of 11 unrelated patients. Excepting 1, all were true homozygotes. Six different variants in LDLR were identified: c.-139delCTCCCCCTGC, p.Glu140Lys, p.Asp360His, p.Asn405Lys, p.Ala755Glyfs*7, and p.Leu759Serfs*6. Of these, p.Asp360His and p.Asn405Lys were detected for the first time in Mexico; p.Leu759Serfs*6 showed to be the most frequent (43.7% of the alleles 7/16), and c.-139delCTCCCCCTGC is a new variant located in the promoter region.

CONCLUSIONS

This work increases knowledge of biochemical and genetic features in Mexican patients with HoFH. A novel mutation in the LDLR gene promoter was detected: c.-139delCTCCCCCTGC, which possibly inhibits its expression.

Prediction of dyslipidemia using gene mutations, family history of diseases and anthropometric indicators in children and adolescents: The CASPIAN-III study

Dyslipidemia, the disorder of lipoprotein metabolism resulting in high lipid profile, is an important modifiable risk factor for coronary heart diseases. It is associated with more than four million worldwide deaths per year. Half of the children with dyslipidemia have hyperlipidemia during adulthood, and its prediction and screening are thus critical. We designed a new dyslipidemia diagnosis system. The sample size of 725 subjects (age 14.66 ± 2.61 years; 48% male; dyslipidemia prevalence of 42%) was selected by multistage random cluster sampling in Iran. Single nucleotide polymorphisms (rs1801177, rs708272, rs320, rs328, rs2066718, rs2230808, rs5880, rs5128, rs2893157, rs662799, and Apolipoprotein-E2/E3/E4), and anthropometric, life-style attributes, and family history of diseases were analyzed. A framework for classifying mixed-type data in imbalanced datasets was proposed. It included internal feature mapping and selection, re-sampling, optimized group method of data handling using convex and stochastic optimizations, a new cost function for imbalanced data and an internal validation. Its performance was assessed using hold-out and 4-foldcross-validation. Four other classifiers namely as supported vector machines, decision tree, and multilayer perceptron neural network and multiple logistic regression were also used. The average sensitivity, specificity, precision and accuracy of the proposed system were 93%, 94%, 94% and 92%, respectively in cross validation. It significantly outperformed the other classifiers and also showed excellent agreement and high correlation with the gold standard. A non-invasive economical version of the algorithm was also implemented suitable for low- and middle-income countries. It is thus a promising new tool for the prediction of dyslipidemia.

Genetics of Dyslipidemia and Ischemic Heart Disease

PURPOSE OF REVIEW

Genetic dyslipidemias contribute to the prevalence of ischemic heart disease. The field of genetic dyslipidemias and their influence on atherosclerotic heart disease is rapidly developing and accumulating increasing evidence. The purpose of this review is to describe the current state of knowledge in regard to inherited atherogenic dyslipidemias. The disorders of familial hypercholesterolemia (FH) and elevated lipoprotein(a) will be detailed. Genetic technology has made rapid advancements, leading to new discoveries in inherited atherogenic dyslipidemias, which will be explored in this review, as well as a description of possible future developments. Increasing attention has come upon the genetic disorders of familial hypercholesterolemia and elevated lipoprotein(a).

RECENT FINDINGS

This review includes new knowledge of these disorders including description of these disorders, their method of diagnosis, their prevalence, their genetic underpinnings, and their effect on the development of cardiovascular disease. In addition, it discusses major advances in genetic technology, including the completion of the human genome sequence, next-generation sequencing, and genome-wide association studies. Also discussed are rare variant studies with specific genetic mechanisms involved in inherited dyslipidemias, such as in the proprotein convertase subtilisin/kexin type 9 (PCSK9) enzyme. The field of genetics of dyslipidemia and cardiovascular disease is rapidly growing, which will result in a bright future of novel mechanisms of action and new therapeutics.

Lysosomal acid lipase deficiency: a form of non-obese fatty liver disease (NOFLD)

INTRODUCTION

With the growing obesity epidemic, nonalcoholic fatty liver disease (NAFLD) is rapidly becoming one of the leading causes of liver disease worldwide. Although obesity is a main risk factor for the development of NAFLD, it can also develop in lean subjects and can be encountered in different clinical setting and in association with an array of genetic, metabolic, nutritional, infectious and drug-induced disorders. Areas covered: This article discusses causes of fatty liver in non-obese subjects focusing on Lysosomal acid lipase deficiency (LAL-D), a commonly overlooked disorder reviewing its prevalence, genetics, pathogenesis, clinical features, diagnosis and treatment. It will also review other causes of non-alcoholic fatty liver disease, which can be encountered in the absence of obesity and metabolic syndrome. Expert commentary: Although the prevalence of LAL-D has been estimated in the range of 1 in 40,000 and 1 in 300,000, this estimate is much more than the identified cases reported in the literature, which suggests that that the disease may be considerably under-diagnosed. There is a pressing need to educate clinicians about the disease, especially with the development of new promising therapeutic modalities.

Precision Cardiovascular Medicine: State of Genetic Testing

In the 15 years following the release of the first complete human genome sequences, our understanding of rare and common genetic variation as determinants of cardiovascular disease susceptibility, prognosis, and therapeutic response has grown exponentially. As such, the use of genomics to enhance the care of patients with cardiovascular diseases has garnered increased attention from clinicians, researchers, and regulatory agencies eager to realize the promise of precision genomic medicine. However, owing to a large burden of "complex" common diseases, emphasis on evidence-based practice, and a degree of unfamiliarity/discomfort with the language of genomic medicine, the development and implementation of genomics-guided approaches designed to further individualize the clinical management of a variety of cardiovascular disorders remains a challenge. In this review, we detail a practical approach to genetic testing initiation and interpretation as well as review the current state of cardiovascular genetic and pharmacogenomic testing in the context of relevant society and regulatory agency recommendations/guidelines.

A 10-year experience using combined lipid-lowering pharmacotherapy in children and adolescents

BACKGROUND

Current pediatric guidelines for heterozygous familial hypercholesterolemia (HeFH) propose pharmacotherapy (PT) with statins from age 8 to 10 years; however, schemes with absorption inhibitors combined with statins, could be started earlier. The aim of the study was to show the 10-year results of a combined treatment protocol.

METHODS

Prospective, descriptive and analytical study. Pediatric patients (n=70; mean age at PT initiation 9.3 years [range, 2-17.5]) with HeFH who required PT between 2005 and 2015 were included. All patients ≥10 years, with LDL >190 mg/dL or >160 mg/dL with one cardiovascular risk factor (CVRF) or >130 mg/dL with two or more CVRF; and those patients 5-10 years and with LDL-C >240 mg/dL or a family history of a cardiovascular event before 40 years, were medicated. After a period on a lipid-lowering diet (LLD), all patients were started on ezetimibe. Patients who did not achieve the treatment goal were given statins. The variables were: age, age at PT initiation, duration of PT, initial LDL-C, mean LDL-C during ezetimibe monodrug therapy, mean LDL-C during combined PT, and percentage of LDL decrease.

RESULTS

LDL-C levels were: Baseline: 235 mg/dL±55; after 3 months on ezetimibe: 167 mg/dL±47 (decrease: -27.62%). In 18 patients who did not reach the treatment goal atorvastatin was added and their LDL-C decreased -41.5% (p: 0.02). Overall, mean final LDL-C was 155 mg/dL±30.4 (range, 98-257) and treatment goals were reached in 74% of the patients. No severe side effects were reported.

CONCLUSIONS

Combined and sequential treatment starting at early ages was shown to be safe and effective over this follow-up period.

Statin therapy across the lifespan: evidence in major age groups

This review provides needed perspective on statin efficacy and safety in individuals under 40, 40-75, and > 75 years of age. Starting with the 2013 ACC-AHA cholesterol guidelines extensive evidence base on randomized controlled trials (RCTs) we added references in the past 5 years that discussed statin efficacy and safety over the life span. In those under 40, statins are primarily used for treatment of severe hypercholesterolemia, often familial, and they are well tolerated. In middle-aged adults, statins have strong evidence for benefit in primary and secondary prevention trials; however, in primary prevention, a clinician-patient risk discussion should precede statin prescription in order to determine appropriate treatment. In those over 75, issues of statin intensity and net benefit loom large as associated comorbidity, polypharmacy, and potential for adverse effects impact the decision to use statins with RCT data strongest in support of use in secondary prevention. Statin drugs have been studied by RCTs in a large number of individuals. In those groups shown to benefit, statins have reduced the risk of atherosclerotic cardiovascular disease with few side effects as compared to controls. This review has detailed considerations that should occur when statins are given to individuals in different age groups.

Global molecular analysis and APOE mutations in a cohort of autosomal dominant hypercholesterolemia patients in France

Autosomal dominant hypercholesterolemia (ADH) is a human disorder characterized phenotypically by isolated high-cholesterol levels. Mutations in the low density lipoprotein receptor (LDLR), APOB, and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes are well known to be associated with the disease. To characterize the genetic background associated with ADH in France, the three ADH-associated genes were sequenced in a cohort of 120 children and 109 adult patients. Fifty-one percent of the cohort had a possible deleterious variant in LDLR, 3.1% in APOB, and 1.7% in PCSK9. We identified 18 new variants in LDLR and 2 in PCSK9. Three LDLR variants, including two newly identified, were studied by minigene reporter assay confirming the predicted effects on splicing. Additionally, as recently an in-frame deletion in the APOE gene was found to be linked to ADH, the sequencing of this latter gene was performed in patients without a deleterious variant in the three former genes. An APOE variant was identified in three patients with isolated severe hypercholesterolemia giving a frequency of 1.3% in the cohort. Therefore, even though LDLR mutations are the major cause of ADH with a large mutation spectrum, APOE variants were found to be significantly associated with the disease. Furthermore, using structural analysis and modeling, the identified APOE sequence changes were predicted to impact protein function.

Exploring the complete mutational space of the LDL receptor LA5 domain using molecular dynamics: linking SNPs with disease phenotypes in familial hypercholesterolemia

Familial hypercholesterolemia (FH), a genetic disorder with a prevalence of 0.2%, represents a high-risk factor to develop cardiovascular and cerebrovascular diseases. The majority and most severe FH cases are associated to mutations in the receptor for low-density lipoproteins receptor (LDL-r), but the molecular basis explaining the connection between mutation and phenotype is often unknown, which hinders early diagnosis and treatment of the disease. We have used atomistic simulations to explore the complete SNP mutational space (227 mutants) of the LA5 repeat, the key domain for interacting with LDL that is coded in the exon concentrating the highest number of mutations. Four clusters of mutants of different stability have been identified. The majority of the 50 FH known mutations (33) appear distributed in the unstable clusters, i.e. loss of conformational stability explains two-third of FH phenotypes. However, one-third of FH phenotypes (17 mutations) do not destabilize the LR5 repeat. Combining our simulations with available structural data from different laboratories, we have defined a consensus-binding site for the interaction of the LA5 repeat with LDL-r partner proteins and have found that most (16) of the 17 stable FH mutations occur at binding site residues. Thus, LA5-associated FH arises from mutations that cause either the loss of stability or a decrease in domain's-binding affinity. Based on this finding, we propose the likely phenotype of each possible SNP in the LA5 repeat and outline a procedure to make a full computational diagnosis for FH.

Genetics of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disorder characterized by elevated low-density lipoprotein (LDL) cholesterol and premature cardiovascular disease, with a prevalence of approximately 1 in 200-500 for heterozygotes in North America and Europe. Monogenic FH is largely attributed to mutations in the LDLR, APOB, and PCSK9 genes. Differential diagnosis is critical to distinguish FH from conditions with phenotypically similar presentations to ensure appropriate therapeutic management and genetic counseling. Accurate diagnosis requires careful phenotyping based on clinical and biochemical presentation, validated by genetic testing. Recent investigations to discover additional genetic loci associated with extreme hypercholesterolemia using known FH families and population studies have met with limited success. Here, we provide a brief overview of the genetic determinants, differential diagnosis, genetic testing, and counseling of FH genetics.

Maternal inheritance does not predict cholesterol levels in children with familial hypercholesterolemia

BACKGROUND AND AIMS

Pregnancy exerts metabolic changes with increasing levels of total cholesterol and triglycerides as prominent features. Maternal hypercholesterolemia may thus contribute to an unfavorable in utero environment potentially influencing the susceptibility of adult cardiovascular disease in the offspring. We investigated the impact of maternal familial hypercholesterolemia (FH) on pre-treatment plasma lipids and C-reactive protein (CRP) levels in non-statin treated FH children.

METHODS

Children with FH (n = 1063) aged between 0 and 19 years were included. Of these, 500 had inherited FH maternally, 563 paternally and 97.6% had a verified FH mutation. Information about inheritance, mutation type and pretreatment levels of blood lipids and CRP was retrieved from the medical records.

RESULTS

There were no significant differences in the plasma levels of lipids and C-reactive protein (CRP) in children with maternal FH compared with children with paternal FH, (0.12 ≤ P ≤ 0.90). Independent of which parent transmitted FH, children with LDL receptor negative mutations had significantly higher levels of total and LDL cholesterol and Apolipoprotein (Apo) B, and lower levels of HDL cholesterol and ApoA1, compared with children with other LDL receptor mutations (P < 0.001).

CONCLUSION

Maternal inheritance of FH was not associated with detectable long-term effects in the offspring's phenotype measured by adverse lipid profiles and increased CRP levels, whereas a LDL receptor negative mutation was associated with an unfavorably phenotype in FH offspring. Our findings do not support the fetal origin of adulthood disease hypothesis, while at the same time not excluding the hypothesis since other pathways leading to atherosclerosis may be involved.

APOE and LDLR Gene Polymorphisms and Dyslipidemia Tracking. Rio de Janeiro Study

BACKGROUND

Studies show an association between changes in apolipoprotein E (ApoE) and LDLR receptor with the occurrence of dyslipidemia.

OBJECTIVES

To investigate the association between polymorphisms of the APOE (ε2, ε3, ε4) and LDLR (A370T) genes with the persistence of abnormal serum lipid levels in young individuals followed up for 17 years in the Rio de Janeiro Study.

METHODS

The study included 56 individuals (35 males) who underwent three assessments at different ages: A1 (mean age 13.30 ± 1.53 years), A2 (22.09 ± 1.91 years) and A3 (31.23 ± 1.99 years). Clinical evaluation with measurement of blood pressure (BP) and body mass index (BMI) was conducted at all three assessments. Measurement of waist circumference (WC) and serum lipids, and analysis of genetic polymorphisms by PCR-RFLP were performed at A2 and A3. Based on dyslipidemia tracking, three groups were established: 0 (no abnormal lipid value at A2 and A3), 1 (up to one abnormal lipid value at A2 or A3) and 2 (one or more abnormal lipid values at A2 and A3).

RESULTS

Compared with groups 0 and 1, group 2 presented higher mean values of BP, BMI, WC, LDL-c and TG (p < 0.01) and lower mean values of HDL-c (p = 0.001). Across the assessments, all individuals with APOE genotypes ε2/ε4 and ε4/ε4 maintained at least one abnormal lipid variable, whereas those with genotype ε2/ε3 did not show abnormal values (χ2 = 16.848, p = 0.032). For the LDLR genotypes, there was no significant difference among the groups.

CONCLUSIONS

APOE gene polymorphisms were associated with dyslipidemia in young individuals followed up longitudinally from childhood.

Recent advances in the understanding and care of familial hypercholesterolaemia: significance of the biology and therapeutic regulation of proprotein convertase subtilisin/kexin type 9

Familial hypercholesterolaemia (FH) is an autosomal co-dominant disorder that markedly raises plasma low-density lipoprotein-cholesterol (LDL-C) concentration, causing premature atherosclerotic coronary artery disease (CAD). FH has recently come under intense focus and, although there is general consensus in recent international guidelines regarding diagnosis and treatment, there is debate about the value of genetic studies. Genetic testing can be cost-effective as part of cascade screening in dedicated centres, but the full mutation spectrum responsible for FH has not been established in many populations, and its use in primary care is not at present logistically feasible. Whether using genetic testing or not, cholesterol screening of family members of index patients with an abnormally raised LDL-C must be used to determine the need for early treatment to prevent the development of CAD. The metabolic defects in FH extend beyond LDL, and may affect triacylglycerol-rich and high-density lipoproteins, lipoprotein(a) and oxidative stress. Achievement of the recommended targets for LDL-C with current treatments is difficult, but this may be resolved by new drug therapies. Lipoprotein apheresis remains an effective treatment for severe FH and, although expensive, it costs less than the two recently introduced orphan drugs (lomitapide and mipomersen) for homozygous FH. Recent advances in understanding of the biology of proprotein convertase subtilisin/kexin type 9 (PCSK9) have further elucidated the regulation of lipoprotein metabolism and led to new drugs for effectively treating hypercholesterolaemia in FH and related conditions, as well as for treating many patients with statin intolerance. The mechanisms of action of PCSK9 inhibitors on lipoprotein metabolism and atherosclerosis, as well as their impact on cardiovascular outcomes and cost-effectiveness, remain to be established.

PCSK9 inhibition to reduce cardiovascular disease risk: recent findings from the biology of PCSK9

PURPOSE OF REVIEW

Review novel insights into the biology of proprotein convertase subtilisin/kexin 9 (PCSK9) that may explain the extreme efficiency of PCSK9 inhibition and the unexpected metabolic effects resulting from PCSK9 monoclonal antibody therapy, and may identify additional patients as target of therapy.

RECENT FINDINGS

For over 20 years, the practical knowledge of cholesterol metabolism has centered around cellular mechanisms, and around the idea that statin therapy is the essential step to control metabolic abnormalities for cardiovascular risk management. This view has been embraced by the recent AHA/ACC guidelines, but is being challenged by recent studies including nonstatin medications and by the development of a new class of cholesterol-lowering agents that seems destined to early US Food and Drug Administration approval. The discovery of PCSK9 - a circulating protein that regulates hepatic low-density lipoprotein (LDL) receptor and serum LDL cholesterol levels - has led to a race for its therapeutic inhibition. Recent findings on PCSK9 regulation and pleiotropic effects will help identify additional patient groups likely to benefit from the inhibitory therapy and unravel the full potential of PCSK9 inhibition therapy.

SUMMARY

Injectable human monoclonal antibodies to block the interaction between PCSK9 and LDL receptor are demonstrating extraordinary efficacy (LDL reductions of up to 70%) and almost the absence of any side-effects. A more moderate effect is seen on other lipoprotein parameters, with the exception of lipoprotein(a) levels. We describe mechanisms that can explain the effect on lipoprotein(a), predict a potential effect on postprandial triglyderides, and suggest a new category of patients for anti-PCSK9 therapy.

Activity-associated effect of LDL receptor missense variants located in the cysteine-rich repeats

BACKGROUND

The LDL receptor (LDLR) is a Class I transmembrane protein critical for the clearance of cholesterol-containing lipoprotein particles. The N-terminal domain of the LDLR harbours the ligand-binding domain consisting of seven cysteine-rich repeats of approximately 40 amino acids each. Mutations in the LDLR binding domain may result in loss of receptor activity leading to familial hypercholesterolemia (FH). In this study the activity of six mutations located in the cysteine-rich repeats of the LDLR has been investigated.

METHODS

CHO-ldlA7 transfected cells with six different LDLR mutations have been used to analyse in vitro LDLR expression, lipoprotein binding and uptake. Immunoblotting of cell extracts, flow cytometry and confocal microscopy have been performed to determine the effects of these mutations. In silico analysis was also performed to predict the mutation effect.

RESULTS AND CONCLUSION

From the six mutations, p.Arg257Trp turned out to be a non-pathogenic LDLR variant whereas p.Cys116Arg, p.Asp168Asn, p.Asp172Asn, p.Arg300Gly and p.Asp301Gly were classified as binding-defective LDLR variants whose effect is not as severe as null allele mutations.

Lysosomal acid lipase deficiency--an under-recognized cause of dyslipidaemia and liver dysfunction

Lysosomal acid lipase deficiency (LAL-D) is a rare autosomal recessive lysosomal storage disease caused by deleterious mutations in the LIPA gene. The age at onset and rate of progression vary greatly and this may relate to the nature of the underlying mutations. Patients presenting in infancy have the most rapidly progressive disease, developing signs and symptoms in the first weeks of life and rarely surviving beyond 6 months of age. Children and adults typically present with some combination of dyslipidaemia, hepatomegaly, elevated transaminases, and microvesicular hepatosteatosis on biopsy. Liver damage with progression to fibrosis, cirrhosis and liver failure occurs in a large proportion of patients. Elevated low-density lipoprotein cholesterol levels and decreased high-density lipoprotein cholesterol levels are common features, and cardiovascular disease may manifest as early as childhood. Given that these clinical manifestations are shared with other cardiovascular, liver and metabolic diseases, it is not surprising that LAL-D is under-recognized in clinical practice. This article provides practical guidance to lipidologists, endocrinologists, cardiologists and hepatologists on how to recognize individuals with this life-limiting disease. A diagnostic algorithm is proposed with a view to achieving definitive diagnosis using a recently developed blood test for lysosomal acid lipase. Finally, current management options are reviewed in light of the ongoing development of enzyme replacement therapy with sebelipase alfa (Synageva BioPharma Corp., Lexington, MA, USA), a recombinant human lysosomal acid lipase enzyme.

Serum proprotein convertase subtilisin/kexin type 9 and cell surface low-density lipoprotein receptor: evidence for a reciprocal regulation

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) modulates low-density lipoprotein (LDL) receptor (LDLR) degradation, thus influencing serum cholesterol levels. However, dysfunctional LDLR causes hypercholesterolemia without affecting PCSK9 clearance from the circulation.

METHODS AND RESULTS

To study the reciprocal effects of PCSK9 and LDLR and the resultant effects on serum cholesterol, we produced transgenic mice expressing human (h) PCSK9. Although hPCSK9 was expressed mainly in the kidney, LDLR degradation was more evident in the liver. Adrenal LDLR levels were not affected, likely because of the impaired PCSK9 retention in this tissue. In addition, hPCSK9 expression increased hepatic secretion of apolipoprotein B-containing lipoproteins in an LDLR-independent fashion. Expression of hPCSK9 raised serum murine PCSK9 levels by 4.3-fold in wild-type mice and not at all in LDLR(-/-) mice, in which murine PCSK9 levels were already 10-fold higher than in wild-type mice. In addition, LDLR(+/-) mice had a 2.7-fold elevation in murine PCSK9 levels and no elevation in cholesterol levels. Conversely, acute expression of human LDLR in transgenic mice caused a 70% decrease in serum murine PCSK9 levels. Turnover studies using physiological levels of hPCSK9 showed rapid clearance in wild-type mice (half-life, 5.2 minutes), faster clearance in human LDLR transgenics (2.9 minutes), and much slower clearance in LDLR(-/-) recipients (50.5 minutes). Supportive results were obtained with an in vitro system. Finally, up to 30% of serum hPCSK9 was associated with LDL regardless of LDLR expression.

CONCLUSIONS

Our results support a scenario in which LDLR represents the main route of elimination of PCSK9 and a reciprocal regulation between these 2 proteins controls serum PCSK9 levels, hepatic LDLR expression, and serum LDL levels.

Pharmacogenetic aspects in familial hypercholesterolemia with the special focus on FHMarburg (FH p.W556R)

Objective

Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder caused by mutations in the low density lipoprotein receptor (LDLR) gene. FH is characterized by elevated plasma LDL cholesterol, premature atherosclerosis, and a high risk of premature myocardial infarction. In general, mutations within LDLR gene can cause five different classes of defects, namely: class I defect: no LDLR synthesis; class II defect: no LDLR transport; class III defect: no low density lipoprotein (LDL) to LDLR binding; class IV defect: no LDLR/LDL internalization; and class V defect: no LDLR recycling. One might expect that both the class of LDLR defect as well as the precise mutation influences the severity of hypercholesterolemia on one hand and the response on drug treatment on the other. To clarify this question we studied the effect of the LDLR mutation p.W556R in two heterozygote subjects.

Results

We found that two heterozygote FH patients with the LDLR mutation p.W556R causing a class II LDLR defect (transport defective LDLR) respond exceedingly well to the treatment with simvastatin 40 mg/ezetimibe 10 mg. There was a LDL cholesterol decrease of 55 and 64%, respectively. In contrast, two affected homozygote p.W556R FH patients, in the mean time undergoing LDL apheresis, had no response to statin but a 15% LDL cholesterol decrease on ezetimibe monotherapy.

Conclusions

The LDLR mutation p.W556R is a frequent and severe class II defect for FH. The affected homozygote FH patients have a total loss of the functional LDLR and—as expected—do not respond on statin therapy and require LDL apheresis. In contrast, heterozygote FH patients with the same LDLR defect respond exceedingly well to standard lipid-lowering therapy, illustrating that the knowledge of the primary LDLR defect enables us to foresee the expected drug effects.

Carotid intima-media thickness in children with CKD: results from the CKiD study

BACKGROUND AND OBJECTIVES

In adults, increased carotid intima-media thickness (cIMT) as assessed by ultrasonography is a valid predictor of cardiovascular events. Children with CKD are known to be at increased cardiovascular risk. This study sought to identify cardiovascular risk factors associated with increased cIMT in children with CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a cross-sectional analysis of cIMT obtained after 12 months of follow-up of 101 children aged 2-18 years with mild to moderate CKD (median GFR 42.9 ml/min per 1.73 m(2)) in the Chronic Kidney Disease in Children cohort study enrolled between April 2005 and September 2009 and 97 healthy pediatric controls between January 2003 and December 2008. An average of six standardized B-mode ultrasound measurements constituted the overall cIMT measurement.

RESULTS

The median cIMT was 0.43 mm (interquartile range, 0.38-0.48) compared with 0.41 mm in healthy controls (P=0.03 for difference). After multivariable adjustment, the median cIMT was 0.02 mm (95% confidence interval [CI], 0.01-0.05) larger than that of the healthy controls. In a multivariable linear regression analysis, dyslipidemia and hypertension were associated with 0.05 mm (95% CI, 0.01-0.08) and 0.04 mm (95% CI, 0.003-0.08) greater mean cIMT, respectively. Body mass index, CKD etiology, GFR, birth weight, pubertal status, calcium, phosphorus, sex, and race were not associated with cIMT.

CONCLUSIONS

cIMT is significantly elevated among children with CKD, as is the prevalence of other cardiovascular risk factors. Of these risk factors, hypertension and dyslipidemia are significantly associated with increased cIMT.

Effect of mutations in LDLR and PCSK9 genes on phenotypic variability in Tunisian familial hypercholesterolemia patients

BACKGROUND

Autosomal dominant hypercholesterolemia (ADH) is commonly caused by mutations in the low-density lipoprotein (LDL) receptor gene (LDLR), in the apolipoprotein B-100 gene (APOB), or in the proprotein convertase subtilisin kexine 9 gene (PCSK9). ADH subjects carrying a mutation in LDLR present highly variable plasma LDL-cholesterol (LDL-C). This variability might be due to environmental factors or the effect of some modifying genes such as PCSK9 and APOE.

AIMS

We investigated the molecular basis of thirteen Tunisian ADH families and attempted to determine the impact of PCSK9 and APOE gene variations on LDL-cholesterol levels and on the variable phenotypic expression of the disease.

METHODS AND RESULTS

Fifty six subjects were screened for mutations in the LDLR gene through direct sequencing. The causative mutation was found to segregate with the disease in each family and a new frameshift mutation, p.Met767CysfsX21, was identified in one family. The distribution of total- and LDL-cholesterol levels, adjusted for age and gender, among homozygous and heterozygous ADH patients varied widely. Within seven families, nine subjects presented low LDL-cholesterol levels despite carrying a mutation in the LDLR gene. To identify the molecular actors underlying this phenotypic variability, the PCSK9 gene was screened using direct sequencing and/or enzymatic restriction analysis, and the apo E genotypes were determined. A new missense variation (p.Pro174Ser) in the PCSK9 gene was identified and characterized as a new putative loss-of-function mutation.

CONCLUSION

Genetic variations in PCSK9 and APOE genes could explain only part of the variability observed in the phenotypic expression in Tunisian ADH patients carrying mutations in the LDLR gene. Other genetic variants and environmental factors very probably act to fully explain this phenotypic variability.

Management of familial hypercholesterolaemia in children and adolescents

Familial hypercholesterolaemia is a disorder of low-density lipoprotein (LDL) cholesterol metabolism, which is associated with the onset of vascular changes associated with coronary heart disease in childhood. This disorder has co-dominant transmission with a prevalence of one in 500 in the general population. Cascade screening is the most effective method of identifying children. Children in the at-risk group should have their cholesterol levels checked between the age of 2 and 10 years. Children with LDL cholesterol levels ≥ 3.4 mmol/L are likely to suffer from this disorder, although at this level there is a significant false positive rate. Molecular genetic testing is available for the LDL receptor gene, APOB gene and the PCSK9 gene. This is the most specific test for familial hypercholesterolaemia but has a false negative rate of 20-50%. Once diagnosed, treatment should be considered in children with an LDL cholesterol level ≥ 4.9 mmol/L. If the child has two other risk factors or a positive family history, this threshold should be lowered to ≥4.1 mmol/L. Guidelines recommend that treatment should be commenced by the age of 10 years, although some advise waiting until menarche in females. Statin therapy is currently recommended as first line treatment. Randomised placebo trials have shown that statin therapy reduces LDL cholesterol levels by 25% and is not associated with increased risk of adverse events. These are short-term studies, and longer follow-up will be required to definitively prove efficacy and safety.

Clan genomics and the complex architecture of human disease

Human diseases are caused by alleles that encompass the full range of variant types, from single-nucleotide changes to copy-number variants, and these variations span a broad frequency spectrum, from the very rare to the common. The picture emerging from analysis of whole-genome sequences, the 1000 Genomes Project pilot studies, and targeted genomic sequencing derived from very large sample sizes reveals an abundance of rare and private variants. One implication of this realization is that recent mutation may have a greater influence on disease susceptibility or protection than is conferred by variations that arose in distant ancestors.

Mechanisms and genetic determinants regulating sterol absorption, circulating LDL levels, and sterol elimination: implications for classification and disease risk

This review integrates historical biochemical and modern genetic findings that underpin our understanding of the low-density lipoprotein (LDL) dyslipidemias that bear on human disease. These range from life-threatening conditions of infancy through severe coronary heart disease of young adulthood, to indolent disorders of middle- and old-age. We particularly focus on the biological aspects of those gene mutations and variants that impact on sterol absorption and hepatobiliary excretion via specific membrane transporter systems (NPC1L1, ABCG5/8); the incorporation of dietary sterols (MTP) and of de novo synthesized lipids (HMGCR, TRIB1) into apoB-containing lipoproteins (APOB) and their release into the circulation (ANGPTL3, SARA2, SORT1); and receptor-mediated uptake of LDL and of intestinal and hepatic-derived lipoprotein remnants (LDLR, APOB, APOE, LDLRAP1, PCSK9, IDOL). The insights gained from integrating the wealth of genetic data with biological processes have important implications for the classification of clinical and presymptomatic diagnoses of traditional LDL dyslipidemias, sitosterolemia, and newly emerging phenotypes, as well as their management through both nutritional and pharmaceutical means.

Increased intima-media thickness of the carotid artery in childhood: a systematic review of observational studies

Increased carotid intima-media thickness (cIMT) in adults may be caused by a childhood exposure to cardiovascular risk factors. We systematically reviewed observational studies to determine whether obesity, insulin-dependent diabetes mellitus (IDDM), dyslipidemia (DL), hypertension (HT), and chronic renal failure (CRF) are associated with increased cIMT in children and adolescent patients compared with control subjects. We performed a PubMed literature search from January 1986 to February 2010. Two reviewers separately verified the inclusion criteria of relevant studies for the objective of the review. The data extracted in the patient and control groups were sample size, age, gender, cIMT measurement methods, cIMT values, and statistical analysis results. From 348 citations, 65 cross-sectional studies (2 cited twice) with case-control design met the inclusion criteria: 26 in obesity, 14 in IDDM, 11 in DL, 8 in HT, and 8 in CRF. cIMT measurement protocols varied according to the studies, with measurements being performed on the common carotid artery in 65/67 cases and on the far wall in 57/67 cases. From the 67 studies cited, 22/26 reported a significantly increased cIMT in obese children and adolescents compared with the control group, 8/14 in IDDM patients, 10/11 in DL patients, 7/8 in HT patients, and 8/8 in CRF patients.

CONCLUSION

Despite the heterogeneity of ultrasound measurement methods, cIMT was significantly increased in 55 out of the 67 cited studies, confirming early vascular damages in pediatric populations with an increased future risk for vascular diseases.