Treatment of pediatric heterozygous familial hypercholesterolemia 7 years after the EAS recommendations: Real-world results from a large French cohort.

BACKGROUND: Heterozygous familial hypercholesterolemia (HeFH) predisposes to premature cardiovascular diseases. Since 2015, the European Atherosclerosis Society has advocated initiation of statins at 8-10 years of age and a low-density lipoprotein cholesterol (LDL-C) target of <135 mg/dL. Longitudinal data from large databases on pharmacological management of pediatric HeFH are lacking. OBJECTIVE: Here, we describe treatment patterns and LDL-C goal attainment in pediatric HeFH using longitudinal real-world data. METHODS: This was a retrospective and prospective multicenter cohort study (2015-2021) of children with HeFH, diagnosed genetically or clinically, aged <18 years, and followed up in the National French Registry of FH (REFERCHOL). Data on the study population as well as treatment patterns and outcomes are summarized as mean±SD. RESULTS: We analyzed the data of 674 HeFH children (age at last visit: 13.1 ± 3.6 years; 82.0 % ≥10 years; 52.5 % females) who were followed up for a mean of 2.8 ± 3.5 years. Initiation of lipid-lowering therapy was on average at 11.8 ± 3.0 years of age for a duration of 2.5 ± 2.8 years. At the last visit, among patients eligible for treatment (573), 36 % were not treated, 57.1 % received statins alone, 6.4 % statins with ezetimibe, and 0.2 % ezetimibe alone. LDL-C was 266±51 mg/dL before treatment and 147±54 mg/dL at the last visit (-44.7 %) in treated patients. Regarding statins, 3.3 %, 65.1 %, and 31.6 % of patients received high-, moderate-, and low-intensity statins, respectively. Overall, 59 % of children on statin therapy alone and 35.1 % on bitherapy did not achieve the LDL-C goal; fewer patients in the older age group did not reach the treatment goal. CONCLUSION: Pediatric patients with FH followed up in specialist lipid clinics in France receive late treatment, undertreatment, or suboptimal treatment and half of them do not reach the therapeutic LDL-C goal. Finding a more efficient framework for linking scientific evidence to clinical practice is needed.

Additive Effect of APOE Rare Variants on the Phenotype of Familial Hypercholesterolemia.

BACKGROUND: Autosomal dominant hypercholesterolemia (ADH) is due to deleterious variants in LDLR, APOB, or PCSK9 genes. Double heterozygote for these genes induces a more severe phenotype. More recently, a new causative variant of heterozygous ADH was identified in APOE. Here we study the phenotype of 21 adult patients, double heterozygotes for rare LDLR and rare APOE variants (LDLR+APOE) in a national wide French cohort. METHODS: LDLR, APOB, PCSK9, and APOE genes were sequenced in 5743 probands addressed for ADH genotyping. The lipid profile and occurrence of premature atherosclerotic cardiovascular diseases were compared between the LDLR+APOE carriers (n=21) and the carriers of the same LDLR causative variants alone (n=22). RESULTS: The prevalence of LDLR+APOE carriers in this French ADH cohort is 0.4%. Overall, LDL (low-density lipoprotein)-cholesterol concentrations were 23% higher in LDLR+APOE patients than in LDLR patients (9.14±2.51 versus 7.43±1.59 mmol/L, P=0.0221). When only deleterious or probably deleterious variants were considered, the LDL-cholesterol concentrations were 46% higher in LDLR+APOE carriers than in LDLR carriers (10.83±3.45 versus 7.43±1.59 mmol/L, P=0.0270). Two patients exhibited a homozygous familial hypercholesterolemia phenotype (LDL-cholesterol >13 mmol/L). Premature atherosclerotic cardiovascular disease was more common in LDLR+APOE patients than in LDLR carriers (70% versus 30%, P=0.026). CONCLUSIONS: Although an incomplete penetrance should be taken into account for APOE variant classification, these results suggest an additive effect of deleterious APOE variants on ADH phenotype highlighting the relevance of APOE sequencing.

APOE Molecular Spectrum in a French Cohort with Primary Dyslipidemia.

Primary hypercholesterolemia is characterized by elevated LDL-cholesterol (LDL-C) levels isolated in autosomal dominant hypercholesterolemia (ADH) or associated with elevated triglyceride levels in familial combined hyperlipidemia (FCHL). Rare APOE variants are known in ADH and FCHL. We explored the APOE molecular spectrum in a French ADH/FCHL cohort of 5743 unrelated probands. The sequencing of LDLR, PCSK9, APOB, and APOE revealed 76 carriers of a rare APOE variant, with no mutation in LDLR, PCSK9, or APOB. Among the 31 APOE variants identified here, 15 are described in ADH, 10 in FCHL, and 6 in both probands. Five were previously reported with dyslipidemia and 26 are novel, including 12 missense, 5 synonymous, 2 intronic, and 7 variants in regulatory regions. Sixteen variants were predicted as pathogenic or likely pathogenic, and their carriers had significantly lower polygenic risk scores (wPRS) than carriers of predicted benign variants. We observed no correlation between LDL-C levels and wPRS, suggesting a major effect of APOE variants. Carriers of p.Leu167del were associated with a severe phenotype. The analysis of 11 probands suggests that carriers of an APOE variant respond better to statins than carriers of a LDLR mutation. Altogether, we show that the APOE variants account for a significant contribution to ADH and FCHL.

Prevalence of familial hypercholesterolaemia in patients presenting with premature acute coronary syndrome.

BACKGROUND: Familial hypercholesterolaemia (FH) is responsible for severe hypercholesterolaemia and premature cardiovascular morbidity and mortality. The first clinical event is typically an acute coronary syndrome. Unfortunately, FH is largely underdiagnosed in the general population. AIMS: To assess the prevalence of clinical FH among patients with premature (aged≤50 years) acute myocardial infarction (MI) and compare it with FH prevalence in a control population. METHODS: We reviewed in our database all patients with premature MI (aged≤50 years) referred to Ambroise Paré Hospital from 2014 to 2018. FH prevalence was estimated via the Dutch Lipid Clinic Network score, based on personal and family history of premature cardiovascular disease and low-density lipoprotein cholesterol concentrations. FH was "possible" with a score between 3 and 5 points, "probable" with a score between 6 and 8 and "definite" with a score above 8. FH prevalence in young patients with MI was then compared with FH prevalence in a general population of the same age from the CARVAR 92 prospective cohort. RESULTS: Of the 457 patients with premature MI, 29 (6%) had "probable" or "definite" FH. In the CARVAR 92 cohort, 16 (0.16%) of 9900 subjects aged≤50 years had "probable" or "definite" FH. FH prevalence was 39 times greater among patients with premature MI than in the control population (P<0.0001). In multivariable analysis, FH was strongly associated with MI (adjusted odds ratio 38.4, 95% confidence interval 19.1-79.4). CONCLUSIONS: FH is>30-fold more common in patients referred for premature MI than in the general population; this highlights the need for FH screening after a first MI to enhance lipid-lowering therapy and allow early identification of family members.

Challenging the traditional approach for interpreting genetic variants: Lessons from Fabry disease.

Fabry disease (FD) is an X-linked genetic disease due to pathogenic variants in GLA. The phenotype varies depending on the GLA variant, alpha-galactosidase residual activity, patient's age and gender and, for females, X chromosome inactivation. Over 1000 variants have been identified, many through screening protocols more susceptible to disclose non-pathogenic variants or variants of unknown significance (VUS). This, together with the non-specificity of some FD symptoms, challenges physicians attempting to interpret GLA variants. The traditional way to interpreting pathogenicity is based on a combined approach using allele frequencies, genomic databases, global and disease-specific clinical databases, and in silico tools proposed by the American College of Medical Genetics and Genomics. Here, a panel of FD specialists convened to study how expertise may compare with the traditional approach. Several GLA VUS, highly controversial in the literature (p.Ser126Gly, p.Ala143Thr, p.Asp313Tyr), were re-analyzed through reviews of patients' charts. The same was done for pathogenic GLA variants with some specificities. Our data suggest that input of geneticists and physicians with wide expertise in disease phenotypes, prevalence, inheritance, biomarkers, alleles frequencies, disease-specific databases, and literature greatly contribute to a more accurate interpretation of the pathogenicity of variants, bringing a significant additional value over the traditional approach.

Posttranscriptional Regulation of the Human LDL Receptor by the U2-Spliceosome.

BACKGROUND: The LDLR (low-density lipoprotein receptor) in the liver is the major determinant of LDL-cholesterol levels in human plasma. The discovery of genes that regulate the activity of LDLR helps to identify pathomechanisms of hypercholesterolemia and novel therapeutic targets against atherosclerotic cardiovascular disease. METHODS: We performed a genome-wide RNA interference screen for genes limiting the uptake of fluorescent LDL into Huh-7 hepatocarcinoma cells. Top hit genes were validated by in vitro experiments as well as analyses of data sets on gene expression and variants in human populations. RESULTS: The knockdown of 54 genes significantly inhibited LDL uptake. Fifteen of them encode for components or interactors of the U2-spliceosome. Knocking down any one of 11 out of 15 genes resulted in the selective retention of intron 3 of LDLR. The translated LDLR fragment lacks 88% of the full length LDLR and is detectable neither in nontransfected cells nor in human plasma. The hepatic expression of the intron 3 retention transcript is increased in nonalcoholic fatty liver disease as well as after bariatric surgery. Its expression in blood cells correlates with LDL-cholesterol and age. Single nucleotide polymorphisms and 3 rare variants of one spliceosome gene, RBM25, are associated with LDL-cholesterol in the population and familial hypercholesterolemia, respectively. Compared with overexpression of wild-type RBM25, overexpression of the 3 rare RBM25 mutants in Huh-7 cells led to lower LDL uptake. CONCLUSIONS: We identified a novel mechanism of posttranscriptional regulation of LDLR activity in humans and associations of genetic variants of RBM25 with LDL-cholesterol levels.

Real-World Efficacy of Proprotein Convertase Subtilisin/Kexin Type 9 Inhibitors (PCSK9i) in Heterozygous Familial Hypercholesterolemia Patients Referred for Lipoprotein Apheresis.

BACKGROUND A small proportion of familial hypercholesterolemia (FH) patients can adequately control this condition, although achieving the recommended targets for low-density lipoprotein cholesterol (LDL-c) levels remains a challenge. Proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) are new and potent lipid-lowering drugs. However, there is scarce literature on real-world data about their use in patients with FH. MATERIAL AND METHODS We examined the reduction in LDL-c levels from the baseline, after PCSK9i initiation in heterozygous familial hypercholesterolemia patients referred for lipoprotein apheresis in our regional lipid clinic. The study was conducted from March 2018 to September 2019, the period immediately after PCSK9i reimbursement was available in France. PCSK9i was added on top of the patients' maximal tolerated lipid-lowering regimens. RESULTS The study had 123 patients with heterozygous FH. The mean age of the patients was 59±11 years. The mean baseline LDL-c for all the participants was 277±78 mg/dl. It was 283±81 mg/dl in the PCSK9i monotherapy group (n=83), 247±68 mg/dl in the PCSK9i plus ezetimibe group (n=12), and 264±78 mg/dl in the PCSK9i plus statin and ezetimibe group (n=28). The mean decrease observed in the LDL-c level from baseline was 136±70 mg/dl (n=123), 125±60 mg/dl (n=83), 103±77 mg/dl (n=12), and 175±70 mg/dl (n=28), respectively. CONCLUSIONS An overall reduction of 49.1% from the baseline LDL-c was observed in the heterozygous FH population after PCSK9i initiation in a real-world experience. The group treated with PCSK9i ezetimibe plus statin showed further reduction of their LDL-c levels with a better responder rate, achieving the target 50% reduction in LDL-c from the baseline.

APOE gene variants in primary dyslipidemia.

Apolipoprotein E (apoE) is a major apolipoprotein involved in lipoprotein metabolism. It is a polymorphic protein and different isoforms are associated with variations in lipid and lipoprotein levels and thus cardiovascular risk. The isoform apoE4 is associated with an increase in LDL-cholesterol levels and thus a higher cardiovascular risk compared to apoE3. Whereas, apoE2 is associated with a mild decrease in LDL-cholesterol levels. In the presence of other risk factors, apoE2 homozygotes could develop type III hyperlipoproteinemia (familial dysbetalipoproteinemia or FD), an atherogenic disorder characterized by an accumulation of remnants of triglyceride-rich lipoproteins. Several rare APOE gene variants were reported in different types of dyslipidemias including FD, familial combined hyperlipidemia (FCH), lipoprotein glomerulopathy and bona fide autosomal dominant hypercholesterolemia (ADH). ADH is characterized by elevated LDL-cholesterol levels leading to coronary heart disease, and due to molecular alterations in three main genes: LDLR, APOB and PCSK9. The identification of the APOE-p.Leu167del variant as the causative molecular element in two different ADH families, paved the way to considering APOE as a candidate gene for ADH. Due to non mendelian interacting factors, common genetic and environmental factors and perhaps epigenetics, clinical presentation of lipid disorders associated with APOE variants often strongly overlap. More studies are needed to determine the spectrum of APOE implication in each of the diseases, notably ADH, in order to improve clinical and genetic diagnosis, prognosis and patient management. The purpose of this review is to comment on these APOE variants and on the molecular and clinical overlaps between dyslipidemias.

A Simple RFLP-Based Method for HFE Gene Multiplex Amplification and Determination of Hereditary Hemochromatosis-Causing Mutation C282Y and H63D Variant with Highly Sensitive Determination of Contamination.

Hereditary hemochromatosis is an autosomal recessive disorder with incomplete penetrance that results from excess iron absorption and can lead to chronic liver disease, fibrosis, cirrhosis, and hepatocellular carcinoma. The most common form of hereditary hemochromatosis in Western Europe is due to a homozygous mutation (p.(Cys282Tyr) or C282Y), in the HFE gene which encodes hereditary haemochromatosis protein. In the general European population, the frequency of the homozygous genotype is 0.4%, and this mutation explains up to 95% of hereditary hemochromatosis in France. We report here an improved PCR and restriction endonuclease assay based on multiplex amplification of HFE exon 4 (for C282Y detection), HFE exon 2 (for H63D detection), FZD1 gene (for digestion controls), and two Short Tandem Repeats (SE33 and FGA) for identity monitoring and contamination tracking. Fluorescent primers allow capillary electrophoresis, accurate allele tagging, and sensitive contamination detection.

High burden of recurrent cardiovascular events in heterozygous familial hypercholesterolemia: The French Familial Hypercholesterolemia Registry.

BACKGROUND AND AIMS: Cardiovascular risk is high in heterozygous familial hypercholesterolemia (HeFH). The objective of this study was to describe recurrent cardiovascular events in selected patients with HeFH attending lipid clinics in France. METHODS: We included 781 patients with a clinical (Dutch Lipid Clinic Network score ≥ 6) or genetic diagnosis of HeFH who had experienced a first cardiovascular event (myocardial infarction, percutaneous coronary intervention or coronary bypass, unstable angina, stroke, peripheral arterial revascularization or cardiovascular death) and were enrolled in the French Familial Hypercholesterolemia Registry (November 2015 to March 2018). RESULTS: The first cardiovascular event occurred at the mean age of 47 years (interquartile range 39-55) in a predominantly male population (72%); 48% of patients were on statin therapy. Overall, 37% of patients had at least one recurrent cardiovascular event (mean of 1.8 events per patient), of which 32% occurred in the 12 months after the index event; 55% of events occurred >3 years after the first event. Mean LDL-C at the last clinic visit was 144 ±â€¯75 mg/dL (132 ±â€¯69 mg/dL for patients on high-potency statin therapy and 223 ±â€¯85 mg/dL for untreated patients). CONCLUSIONS: The rate of recurrent cardiovascular events was high in French patients with HeFH in secondary prevention. The detection of FH during childhood is crucial to prevent CV events at a young age by early initiating statin therapy. There is a clear urgent need to expand the actual very small target population which can be treated with the PCSK9 inhibitor in France.

[Familial hypercholesterolemia: An under-diagnosed and under-treated disease. Survey of 495 physicians]. / Hypercholestérolémie familiale peu diagnostiquée, insuffisamment traitée. Enquête auprès de 495 médecins.

INTRODUCTION: Heterozygous familial hypercholesterolemia (FH) is one of the most frequent genetic diseases with a prevalence of 1/250. It is characterized by a very high cholesterol level since birth and is often complicated by cardiovascular diseases (CV) in young patients. While early diagnosis and appropriate therapeutic management can avoid CV complications, HF is largely under-diagnosed and therefore under-treated. METHODS: To investigate the management of HF in France, we conducted a survey with 495 general practitioners (n=200) and specialists (n=295). RESULTS: The results revealed: a large underestimation of the CV risk and a high therapeutic inertia in the management of the affected patients. The practitioners reported a real need for more information about the disease. CONCLUSION: Given the high frequency of HF and the associated cardiovascular morbidity and mortality, general practitioners have a decisive role to play for the identification and the management of these patients. The recent publication of HAS recommendations on family screening procedures and care of HF patients should improve the management of this disease.

Genetic diagnosis of familial hypercholesterolemia is associated with a premature and high coronary heart disease risk.

BACKGROUND: Familial hypercholesterolemia (FH) is a common autosomal dominant disease associated with premature coronary heart disease (CHD). Studies tend to show that patients with FH associated with an identified mutation (mutation+ FH) are at higher risk than patients without an identified mutation (mutation- FH). We compared the clinical and biological profile and the risk of CHD in patients with mutation+ FH and mutation- FH. HYPOTHESIS: In addition to LDL-C, a pathogenic mutation predicts premature CHD in FH. METHODS: We successively included all patients with suspected FH (LDL-C > 190 mg/dL if age > 18 years; LDL-C > 160 mg/dL if age < 18 years) and compared patients with a pathogenic mutation with those without an identified pathogenic mutation. RESULTS: We studied 179 patients with mutation+ FH and 147 with mutation- FH. The mean age was 44 (± 18) years. The lipid profile was more atherogenic in those with mutation+ FH, who had higher LDL-C (254 ± 69 mg/dL vs 218 ± 35 mg/dL; P < 0.01) and lower HDL-C (53 ± 14 mg/dL vs 58 ± 17 mg/dL; P < 0.01). Despite the more atherogenic nonlipid cardiovascular profile of patients with mutation- FH, the age of CHD onset was earlier in patients with mutation+ FH (48 vs 56 years; P = 0.026). After multiple adjustment, the presence of a positive mutation was significantly associated with premature CHD (OR: 3.0, 95% CI: 1.38-6.55, P < 0.01). CONCLUSIONS: Patients with mutation+ FH have a more atherogenic lipid profile and a 3-fold higher risk of premature CHD, as well as earlier onset of CHD, than patients with mutation- FH.

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

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

Familial hypercholesterolemia: experience from France.

PURPOSE OF REVIEW: We provide an overview of molecular diagnosis for familial hypercholesterolemia in France including descriptions of the mutational spectrum, polygenic susceptibility and perspectives for improvement in familial hypercholesterolemia diagnosis. RECENT FINDINGS: Molecular testing for familial hypercholesterolemia is recommended for patients with a LDL-cholesterol level above 190 mg/dl (adults) associated with criteria related to personal and family history of hypercholesterolemia and premature cardiovascular disease. Among the 3381 index cases included with these characteristics in the French registry for familial hypercholesterolemia, 2054 underwent molecular diagnosis and 1150 (56%) were found to have mutations (93.5% in LDL Receptor (LDLR), 4.7% in apolipoprotein B and 1.8% in Proprotein convertase subtilisin/kexin type 9). A total of 416 different pathogenic variants were found in the LDLR gene. Based on gene score calculation, a polygenic origin may be suggested in 36% of nonmutated patients. Involvement of genetic counselors and education of healthcare professionals for genetics of familial hypercholesterolemia are underway with the aim of improving the efficiency of the diagnosis. SUMMARY: Genetic cascade screening for familial hypercholesterolemia is currently implemented in France with the complexity to address the diversity of its molecular cause in index cases. Optimization of patient care pathways is critical to improve both the rate of diagnosis and the management of familial hypercholesterolemia patients.

Characterization of Autosomal Dominant Hypercholesterolemia Caused by PCSK9 Gain of Function Mutations and Its Specific Treatment With Alirocumab, a PCSK9 Monoclonal Antibody.

BACKGROUND: Patients with PCSK9 gene gain of function (GOF) mutations have a rare form of autosomal dominant hypercholesterolemia. However, data examining their clinical characteristics and geographic distribution are lacking. Furthermore, no randomized treatment study in this population has been reported. METHODS AND RESULTS: We compiled clinical characteristics of PCSK9 GOF mutation carriers in a multinational retrospective, cross-sectional, observational study. We then performed a randomized placebo-phase, double-blind study of alirocumab 150 mg administered subcutaneously every 2 weeks to 13 patients representing 4 different PCSK9 GOF mutations with low-density lipoprotein cholesterol (LDL-C) ≥70 mg/dL on their current lipid-lowering therapies at baseline. Observational study: among 164 patients, 16 different PCSK9 GOF mutations distributed throughout the gene were associated with varying severity of untreated LDL-C levels. Coronary artery disease was common (33%; average age of onset, 49.4 years), and untreated LDL-C concentrations were higher compared with matched carriers of mutations in the LDLR (n=2126) or apolipoprotein B (n=470) genes. Intervention study: in PCSK9 GOF mutation patients randomly assigned to receive alirocumab, mean percent reduction in LDL-C at 2 weeks was 62.5% (P<0.0001) from baseline, 53.7% compared with placebo-treated PCSK9 GOF mutation patients (P=0.0009; primary end point). After all subjects received 8 weeks of alirocumab treatment, LDL-C was reduced by 73% from baseline (P<0.0001). CONCLUSIONS: PCSK9 GOF mutation carriers have elevated LDL-C levels and are at high risk of premature cardiovascular disease. Alirocumab, a PCSK9 antibody, markedly lowers LDL-C levels and seems to be well tolerated in these patients. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique Identifier: NCT01604824.

Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation.

Apolipoprotein (apo) E mutants are associated with type III hyperlipoproteinemia characterized by high cholesterol and triglycerides levels. Autosomal dominant hypercholesterolemia (ADH), due to the mutations in the LDLR, APOB, or PCSK9 genes, is characterized by an isolated elevation of cholesterol due to the high levels of low-density lipoproteins (LDLs). We now report an exceptionally large family including 14 members with ADH. Through genome-wide mapping, analysis of regional/functional candidate genes, and whole exome sequencing, we identified a mutation in the APOE gene, c.500_502delTCC/p.Leu167del, previously reported associated with sea-blue histiocytosis and familial combined hyperlipidemia. We confirmed the involvement of the APOE p.Leu167del in ADH, with (1) a predicted destabilization of an alpha-helix in the binding domain, (2) a decreased apo E level in LDLs, and (3) a decreased catabolism of LDLs. Our results show that mutations in the APOE gene can be associated with bona fide ADH.

Genomic characterization of two deletions in the LDLR gene in Tunisian patients with familial hypercholesterolemia.

Autosomal Dominant Hypercholesterolemia (ADH) is due to defects in the LDL receptor gene (LDLR), the apolipoprotein B-100 gene (APOB) or the proprotein convertase subtilisin/kexin type 9 gene (PCSK9). The aim of this study was to identify and to characterize the ADH-causative mutations in two Tunisian families. Analysis of the LDLR gene was performed by direct sequencing, multiplex ligation-dependent probe amplification (MLPA) and by long range PCR and sequencing. The PCSK9 gene was analysed by direct sequencing and the APOB gene was screened for the most common mutation: p.Arg3527Gln. In the LDLR gene, we found two large deletions and characterized their exact extent and breakpoint sequences. The first one is a deletion of 12,684 bp linking intron 1 to intron 5: g.11205052_11217736del12684. The second deletion spans 2364 bp from intron 4 to 6: g.11216885_11219249del2364. Sequence analysis of each deletion breakpoint indicates that intrachromatid non-allelic homologous recombination (NAHR) between Alu elements is involved. These two large rearrangements in the LDLR gene are the first to be described in the Tunisian population, increasing the spectrum of ADH-causative mutations.

Identification and characterization of new gain-of-function mutations in the PCSK9 gene responsible for autosomal dominant hypercholesterolemia.

BACKGROUND: The identification of mutations in PCSK9 (proprotein convertase subtilisin kexin9) in autosomal dominant hypercholesterolemia (ADH), has revealed the existence of a new player in cholesterol homeostasis. PCSK9 has been shown to enhance the degradation of the LDL receptor (LDLR) at the cell surface. Gain-of-function mutations of PCSK9 induce ADH and are very rare, but their identification is crucial in studying PCSK9's role in hypercholesterolemia, its detailed trafficking pathway and its impact on the LDLR. METHODS: In order to identify new mutations and understand the exact mechanisms of action of mutated PCSK9, PCSK9 was sequenced in 75 ADH patients with no mutations in the LDLR or APOB genes. Functional analyses in cell culture were conducted and the impact of novel PCSK9 mutations on the quantitative and qualitative features of lipoprotein particles and on the HDL-mediated cellular cholesterol efflux was studied. RESULTS: Among these 75 ADH probands with no mutations in the LDLR or APOB genes, four gain-of-function mutations of PCSK9 were identified, of which two were novel: the p.Leu108Arg and the p.Asp35Tyr substitutions. In vitro studies of their consequences on the activity of PCSK9 on cell surface levels of LDLR showed that the p.Leu108Arg mutation clearly results in a gain-of-function, while the p.Asp35Tyr mutation created a novel Tyr-sulfation site, which may enhance the intracellular activity of PCSK9. CONCLUSION: These data further contribute to the characterization of PCSK9 mutations and to better understanding of the impact on cholesterol metabolism of this new therapeutic target.

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.

Molecular spectrum of autosomal dominant hypercholesterolemia in France.

Autosomal Dominant Hypercholesterolemia (ADH), characterized by isolated elevation of plasmatic LDL cholesterol and premature cardiovascular complications, is associated with mutations in 3 major genes: LDLR (LDL receptor), APOB (apolipoprotein B) and PCSK9(proprotein convertase subtilisin-kexin type 9). Through the French ADH Research Network, we collected molecular data from 1358 French probands from eleven different regions in France.Mutations in the LDLR gene were identified in 1003 subjects representing 391 unique events with 46.0% missense, 14.6% frameshift, 13.6% splice, and 11.3% nonsense mutations, 9.7% major rearrangements, 3.8% small in frame deletions/insertions, and 1.0% UTR mutations. Interestingly,175 are novel mutational events and represent 45% of the unique events we identified, highlighting a specificity of the LDLR mutation spectrum in France. Furthermore, mutations in the APOB gene were identified in 89 probands and in the PCSK9 gene in 10 probands. Comparison of available clinical and biochemical data showed a gradient of severity for ADH-causing mutations:FH=PCSK9>FDB>«Others¼ genes. The respective contribution of each known gene to ADH inthis French cohort is: LDLR 73.9%, APOB 6.6%, PCSK9 0.7%. Finally, in 19.0% of the probands,no mutation was found, thus underscoring the existence of ADH mutations located in still unknown genes.