Autosomal Dominant Hypercholesterolemia Research Articles

The singular French PCSK9-p.Ser127Arg gain-of-function variant: A significant player in cholesterol levels from a 775-year-old common ancestor

Background and aimsPCSK9 is a key regulator of LDL-cholesterol levels. PCSK9 gain of function variants (GOFVs) cause autosomal dominant hypercholesterolemia (ADH). The first described PCSK9-GOFV, p.Ser127Arg, almost exclusively reported in France, represents 67 % of the PCSK9 French GOFVs due to a founder effect. Few other carriers are reported in South Africa and Norway. This study aims to estimate when the common ancestor lived and to describe a cohort of p.Ser127Arg carriers. MethodsEight families and 14 p.Ser127Arg carriers were genotyped and phenotyped. Haplotypes were constructed using 11 microsatellites around PCSK9 and 6 intragenic single nucleotide polymorphisms (SNPs). To add to the biological analysis, eight additional p.Ser127Arg carriers, 12 carriers of other PCSK9-GOFVs, 93 LDLR loss of function variant (LOFV) carriers and 49 non-carriers subjects were phenotyped. ResultsThe most common ancestor of p.Ser127Arg was estimated to have lived 775 years ago [95 % CI: 575-1075]. French Protestants exiled after the revocation of the Edict of Nantes in 1685 AD likely brought the variant to South Africa and Norway. As expected for ADH subjects, carriers of LDLR-LOFV, the p.Ser127Arg, or other PCSK9-GOFVs showed significantly higher LDL-C levels than that of the non-carriers. Interestingly, LDL-C levels are higher for LDLR-LOFVs and for the reduced secreted p.Ser127Arg than for secreted PCSK9-GOFVs, suggesting a greater effect of the p.Ser127Arg. Conversely, HDL-C was significantly lower for LDLR-LOFV and p.Ser127Arg carriers. ConclusionsThis first report from a large cohort of PCSK9-p.Ser127Arg carriers provides observations suggesting a stronger hypercholesterolemic potential of the mutated pro-PCSK9 compared with the secreted mature protein. This work also provides additional data to support the association between PCSK9 and HDL metabolism, and molecular evidence that this variant appeared in France around 1248 AD (Graphical Abstract = Fig. 1).

Rare variants in U2-spliceosome genes are involved in autosomal dominant hypercholesterolemia

Rare variants in U2-spliceosome genes are involved in autosomal dominant hypercholesterolemia

APOE and familial hypercholesterolemia.

Autosomal dominant hypercholesterolemia is a common cause of cardiovascular disease. In addition to the classic genes that cause hypercholesterolemia, LDLR, APOB and PCSK9 , a new locus has emerged as a candidate to be the cause of this hyperlipidemia, the p.(Leu167del) mutation in the APOE gene. Various studies have demonstrated the involvement of the p.(Leu167del) mutation in the APOE gene in hypercholesterolemia: Studies of family segregation, lipoprotein composition by ultracentrifugation and proteomic techniques, and functional studies of VLDL-carrying p.(Leu167del) internalization with cell cultures have demonstrated the role of this mutation in the cause of hypercholesterolemia. The phenotype of individuals carrying the p.(Leu167del) in APOE is indistinguishable from familial hypercholesterolemia individuals with mutations in the classic genes. However, a better response to lipid-lowering treatment has been demonstrated in these APOE mutation carrier individuals. Therefore, APOE gene should be considered a candidate locus along with LDLR, APOB , and PCSK9 to be investigated in the genetic diagnosis of familial hypercholesterolemia.

Modelling a two-stage adult population screen for autosomal dominant familial hypercholesterolaemia: cross-sectional analysis within the UK Biobank

BackgroundMost people with autosomal dominant familial hypercholesterolaemia (FH) remain undetected, which represents a missed opportunity for coronary heart disease prevention.ObjectiveTo evaluate the performance of two-stage adult population screening for FH.DesignUsing...

Integrated omics approach for the identification of HDL structure-function relationships in PCSK9-related familial hypercholesterolemia

The role of proprotein convertase subtilisin/kexin type 9 (PCSK9) in dyslipidemia may go beyond its immediate effects on low-density lipoprotein receptor (LDL-R) activity. This study aimed to assess PCSK9-derived alterations of high-density lipoprotein (HDL) physiology, which bear a potential to contribute to cardiovascular risk profile. HDL was isolated from 33 patients with familial autosomal dominant hypercholesterolemia (FH), including those carrying PCSK9 gain-of-function (GOF) genetic variants (FH-PCSK9, n=11), together with two groups of dyslipidemic patients employed as controls and carrying genetic variants in the LDL-R not treated (ntFH-LDLR, n=11) and treated (tFH-LDLR, n=11) with statins, and 11 normolipidemic controls. Biological evaluations paralleled by proteomic, lipidomic and glycomic analyses were applied to characterize functional and compositional properties of HDL. Multiple deficiencies in the HDL function were identified in the FH-PCSK9 group relative to dyslipidemic FH-LDLR patients and normolipidemic controls, which involved reduced antioxidative, antiapoptotic, anti-thrombotic and anti-inflammatory activities. By contrast, cellular cholesterol efflux capacity of HDL was unchanged. In addition, multiple alterations of the proteomic, lipidomic and glycomic composition of HDL were found in the FH-PCSK9 group. Remarkably, HDLs from FH-PCSK9 patients were systematically enriched in several lysophospholipids as well as in A2G2S2 (GP13) glycan and apolipoprotein A-IV. Based on network analysis of functional and compositional data, a novel mosaic structure-function model of HDL biology involving FH was developed. Several metrics of anti-atherogenic HDL functionality are altered in FH-PCSK9 patients paralleled by distinct compositional alterations. These data provide a first-ever overview of the impact of GOF PCSK9 genetic variants on structure-function relationships in HDL.

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

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. 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). 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). 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.

A novel angiogenic effect of PCSK9- regulated genes

BackgroundSince the discovery of the Proprotein Convertase Subtilisin/Kexin Type 9(PCSK9) gene has been involved in regulating low-density lipoprotein metabolism and cardiovascular disease (CVD), many therapeutic strategies directly targeting PCSK9 have been introduced. PCSK9 gain of function (GoF) mutations are associated with autosomal dominant hypercholesterolemia (ADH) and premature atherosclerosis. In contrast, PCSK9 loss of function (LOF) mutations have cardioprotective effects and can lead to familial hypo cholesterol in some instances. However, its potential impacts beyond the typical effects on lipid metabolism have not been elucidated. Therefore the study aimed to identify and verify PCSK9′s possible effects beyond its traditional role in lipid metabolism. MethodsThe S127R is a PCSK9 gain of function mutation. Firstly, We used the data of the gene expression Omnibus(GEO) database to identify the differentially expressed genes between S127R mutation carriers and ordinary people. Secondly, the identification and analysis of significant genes were performed with various bioinformatics programs. Thirdly, to verify the possible effect and the potential pathways of PCSK9 on angiogenesis, we constructed PCSK9 low and high expression models by transfecting PCSK9-siRNA (small interfering RNA) and PCSK9-plasmid complex into human umbilical vein endothelial cells (HUVECs), respectively. Furthermore, Wound-Healing Assay and Capillary tube formation assay were applied to measure the effect of PCSK9 on angiogenesis. Fourthly, the expression level of VEGFR2 and the significant genes between PCSK9 low and high expression models were verified by quantitative real-time PCR. All data were analysed by GraphPad Prism 8 software. Results88 DEGs were identified, including 45 up-regulated and 43 down-regulated DEGs. Furthermore, we identified the six genes (MMP9, CASP3, EGR1, NGFR, LEFTY1 and NODAL) as significantly different genes between PCSK9-S127R and Control hiPSC. Further, we found that these significant difference genes were mainly associated with angiogenesis after enrichment analysis. To verify the possible effect of PCSK9 on angiogenesis, we constructed low and high-expression PCSK9 models by transfecting siRNA and PCSK9-plasmid complex into human umbilical vein endothelial cells (HUVECs), respectively. The tubule formation test and Wound healing assays showed that overexpression of PCSK9 had an inhibitory effect on angiogenesis, which could be reversed by decreasing the expression of PCSK9. Moreover, bioinformatics analysis indicated that the six hub genes (MMP9, CASP3, EGR1, NGFR, LEFTY1 and NODAL) might play a vital role in the biological function of PCSK9 in angiogenesis. Real-time quantitative PCR was applied to clarify the expression profiles of these critical genes in overexpression/knockdown PCSK9. Finally, the expression levels of MMP9, Caspase3, LEFTY1, and NODAL were suppressed by overexpression of PCSK9 and could be alleviated by PCSK9 knockdown. Otherwise, EGR1 had the opposite expression trend, and there was no specific trend of NGFR after repeated experiments. ConclusionPCSK9 might play an essential role in angiogenesis, unlike its typical role in lipid metabolism, and MMP9, Caspase3, LEFTY1, NODAL, and EGR1 may be involved in the regulation of angiogenesis as critical genes.

Modelling a two-stage screen for autosomal dominant familial hypercholesterolaemia (FH) in UK Biobank

Modelling a two-stage screen for autosomal dominant familial hypercholesterolaemia (FH) in UK Biobank

Whole exome/genome sequencing joint analysis in a family with oligogenic familial hypercholesterolemia

Background and Aims : Autosomal Dominant Hypercholesterolemia (ADH) is a genetic disorder caused by pathogenic variants in LDLR, APOB, PCSK9 and APOE genes. We sought to identify a new candidate gene responsible of the ADH phenotype in patients with no pathogenic variants in known ADH causing genes.

Identifying molecular defects in Swedish patients with FH: No influence of polygenic LDL cholesterol SNP-score

Background and Aims : Even in well characterized patients with a clinical diagnosis of autosomal dominant familial hypercholesterolemia (FH), mutations in the classical FH-related genes (LDLR, APOB, or PCSK9) are not identified in ∼20% of those examined genetically. This indicates that the FH phenotype can be caused by additional inherited abnormalities such as heterozygous mutations in still unknown genes, or epigenetic mechanisms. An alternative hypothesis has been proposed by Talmud et al. [Lancet 2013; 381:1293] who suggest that a substantial fraction of such “mutation-negative” (M-) FH cases could be explained by polygenic inheritance.

Chasing LDL cholesterol to the bottom — PCSK9 in perspective

Low-density lipoprotein (LDL) indubitably contributes causally to atherosclerosis, a leading challenge to health worldwide. Interventions that lower LDL cholesterol (LDL-C) have made remarkable inroads against this global scourge. Recent therapeutic advances have achieved ever lower levels of LDL-C. Improved cardiovascular outcomes continue to accrue from these interventions. In particular, the discovery of the role of proprotein convertase subtilisin/kexin type 9 (PCSK9) as the causal gene in autosomal-dominant hypercholesterolemia has led with remarkable speed to the development of novel agents to lower LDL-C concentrations beyond prior measures, and to alleviate further cardiovascular risk. We review how this story, and its position in the broader landscape of therapy to prevent atherosclerotic events, represents a notable victory of contemporary cardiovascular medicine and reflects successful partnerships between basic scientists, the pharmaceutical and biotechnology sectors, and clinical investigators. Continued cooperation in this manner promises to yield further progress in combating cardiovascular diseases beyond interventions on LDL-C. Libby and Tokgözoğlu discuss the management of atherogenic lipoproteins, notably low-density lipoprotein, with an emphasis on the role of strategies that target PCSK9.

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.

Leu22_Leu23 Duplication at the Signal Peptide of PCSK9 Promotes Intracellular Degradation of LDLr and Autosomal Dominant Hypercholesterolemia.

PCSK9 (Proprotein convertase subtilisin/kexin type 9) regulates LDL-C (low-density lipoprotein cholesterol) metabolism by targeting LDLr (LDL receptor) for lysosomal degradation. PCSK9 gain-of-function variants cause autosomal dominant hypercholesterolemia by reducing LDLr levels, the D374Y variant being the most severe, while loss-of-function variants are associated with low LDL-C levels. Gain-of-function and loss-of-function activities have also been attributed to variants occurring in the PCSK9 signal peptide. Among them, L11 is a very rare PCSK9 variant that seems to increase LDL-C values in a moderate way causing mild hypercholesterolemia. Using molecular biology and biophysics methodologies, activities of L8 and L11 variants, both located in the leucine repetition stretch of the signal peptide, have been extensively characterized in vitro. L8 variant is not associated with increased LDLr activity, whereas L11 activity is increased by ≈20% compared with wt PCSK9. The results suggest that the L11 variant reduces LDLr levels intracellularly by a process resulting from impaired cleavage of the signal peptide. This would lead to less efficient LDLr transport to the cell membrane and promote LDLr intracellular degradation. Deletion of a leucine in the signal peptide in L8 variant does not affect PCSK9 activity, whereas the leucine duplication in the L11 variant enhances LDLr intracellular degradation. These findings highlight the importance of deep in vitro characterization of PCSK9 genetic variants to determine pathogenicity and improve clinical diagnosis and therapy of inherited familial hypercholesterolemia disease.

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

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

A Systematic Approach to Assess the Activity and Classification of PCSK9 Variants.

Background: Gain of function (GOF) mutations of PCSK9 cause autosomal dominant familial hypercholesterolemia as they reduce the abundance of LDL receptor (LDLR) more efficiently than wild-type PCSK9. In contrast, PCSK9 loss of function (LOF) variants are associated with a hypocholesterolemic phenotype. Dozens of PCSK9 variants have been reported, but most remain of unknown significance since their characterization has not been conducted. Objective: Our aim was to make the most comprehensive assessment of PCSK9 variants and to determine the simplest approach for the classification of these variants. Methods: The expression, maturation, secretion, and activity of nine well-established PCSK9 variants were assessed in transiently transfected HEK293 cells by Western blot and flow cytometry. Their extracellular activities were determined in HepG2 cells incubated with the purified recombinant PCSK9 variants. Their binding affinities toward the LDLR were determined by solid-phase immunoassay. Results: LDLR expression increased when cells were transfected with LOF variants and reduced when cells were transfected with GOF variants compared with wild-type PCSK9. Extracellular activities measurements yielded exactly similar results. GOF and LOF variants had increased, respectively reduced, affinities for the LDLR compared with wild-type PCSK9 with the exception of one GOF variant (R218S) that showed complete resistance to inactivation by furin. All variants were expressed at similar levels and underwent normal maturation and secretion patterns except for two LOF and two GOF mutants. Conclusions: We propose that transient transfections of HEK293 cells with a plasmid encoding a PCSK9 variant followed by LDLR expression assessment by flow cytometry is sufficient to reliably determine its GOF or LOF status. More refined experiments should only be used to determine the underlying mechanism(s) at hand.

The importance of cascade genetic screening for diagnosing autosomal dominant hypercholesterolemia: Results from twenty years of a national screening program in Norway

BackgroundThe most cost-effective strategy to diagnose patients with autosomal dominant hypercholesterolemia (ADH) is to perform cascade genetic screening. ObjectiveTo present the cascade genetic screening program for ADH in Norway. MethodsA national cascade genetic screening program for ADH in Norway has been operating at Unit for Cardiac and Cardiovascular Genetics, Oslo University Hospital for twenty years. This program has been run by just one genetic counsellor. We now present the main findings of this cascade genetic screening program. ResultsAfter genetic counselling, 8182 at-risk relatives have consented to genetic testing for the mutation that causes ADH in the family. Of these, 3076 (37.6%) relatives have tested positive. Among mutation-positive relatives 31.3% were on lipid-lowering therapy at the time of genetic testing. However, only 9.8% of these relatives had a value for low density lipoprotein (LDL) cholesterol below 2.5 mmol/l (97 mg/dl). At follow-up six months after genetic testing, reductions in the levels of total serum cholesterol and LDL cholesterol of 12% and 17%, respectively were observed. A total of 8811 ADH heterozygotes have been diagnosed in Norway. Thus, the number of patients diagnosed by this modest cascade genetic screening program constitutes 35% of all Norwegian ADH patients provided with a molecular genetic diagnosis. ConclusionCascade genetic screening for ADH is very effective and should be organized at a national level. Even a modest cascade genetic screening program with small resources, can result in a large number of patients being identified.

Molecular genetic testing for autosomal dominant hypercholesterolemia in 29,449 Norwegian index patients and 14,230 relatives during the years 1993–2020

Background and aimsIn this study, we present the status regarding molecular genetic testing for mutations in the genes encoding the low density lipoprotein receptor (LDLR), apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9) as causes of autosomal dominant hypercholesterolemia (ADH) in Norway. MethodsWe have extracted data from the laboratory information management system at Unit for Cardiac and Cardiovascular Genetics, Oslo University Hospital for the period 1993–2020. This laboratory is the sole laboratory performing molecular genetic testing for ADH in Norway. ResultsA total of 29,449 unrelated hypercholesterolemic patients have been screened for mutations in the LDLR gene, in the APOB gene and in the PCSK9 gene. Of these, 2818 (9.6%) were heterozygotes and 11 were homozygotes or compound heterozygotes. Most of the 264 different mutations identified were found in the LDLR gene. Only two and three mutations were found in the APOB gene or in the PCSK9 gene, respectively. Several founder mutations were identified. After testing of 14,230 family members, a total of 8811 heterozygous patients have been identified. Of these, 94.0% had a mutation in the LDLR gene, 5.4% had a mutation in the APOB gene and 0.6% had a mutation in the PCSK9 gene. ConclusionsA large proportion of Norwegian ADH patients have been provided with a molecular genetic diagnosis. Norway is probably only second to the Netherlands in this respect. A molecular genetic diagnosis may form the basis for starting proper preventive measures and for identifying affected family members by cascade genetic screening.

PCSK9 Variants in Familial Hypercholesterolemia: A Comprehensive Synopsis.

Autosomal dominant familial hypercholesterolemia (FH) affects approximately 1/250, individuals and potentially leads to elevated blood cholesterol and a significantly increased risk of atherosclerosis. Along with improvements in detection and the increased early diagnosis and treatment, the serious burden of FH on families and society has become increasingly apparent. Since FH is strongly associated with proprotein convertase subtilisin/kexin type 9 (PCSK9), increasing numbers of studies have focused on finding effective diagnostic and therapeutic methods based on PCSK9. At present, as PCSK9 is one of the main pathogenic FH genes, its contribution to FH deserves more explorative research.

Polygenic Markers in Patients Diagnosed of Autosomal Dominant Hypercholesterolemia in Catalonia: Distribution of Weighted LDL-c-Raising SNP Scores and Refinement of Variant Selection.

Familial hypercholesterolemia (FH) is associated with mutations in the low-density lipoprotein (LDL) receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin 9 (PCSK9) genes. A pathological variant has not been identified in 30–70% of clinically diagnosed FH patients, and a burden of LDL cholesterol (LDL-c)-raising alleles has been hypothesized as a potential cause of hypercholesterolemia in these patients. Our aim was to study the distribution of weighted LDL-c-raising single-nucleotide polymorphism (SNP) scores (weighted gene scores or wGS) in a population recruited in a clinical setting in Catalonia. The study included 670 consecutive patients with a clinical diagnosis of FH and a prior genetic study involving 250 mutation-positive (FH/M+) and 420 mutation-negative (FH/M−) patients. Three wGSs based on LDL-c-raising variants were calculated to evaluate their distribution among FH patients and compared with 503 European samples from the 1000 Genomes Project. The FH/M− patients had significantly higher wGSs than the FH/M+ and control populations, with sensitivities ranging from 42% to 47%. A wGS based only on the SNPs significantly associated with FH (wGS8) showed a higher area under the receiver operating characteristic curve, and higher diagnostic specificity and sensitivity, with 46.4% of the subjects in the top quartile. wGS8 would allow for the assignment of a genetic cause to 66.4% of the patients if those with polygenic FH are added to the 37.3% of patients with monogenic FH. Our data indicate that a score based on 8 SNPs and the75th percentile cutoff point may identify patients with polygenic FH in Catalonia, although with limited diagnostic sensitivity and specificity.

Homozygous familial hypercholesterolemia in Italy: Clinical and molecular features

Background and aimsHomozygous familial hypercholesterolemia (HoFH) is a rare genetic disorder characterized by extremely elevated plasma levels of low density lipoprotein cholesterol (LDL-C) and high risk of premature atherosclerotic cardiovascular disease (ASCVD). HoFH is caused by pathogenic variants in several genes, such as LDLR, APOB and PCSK9, responsible for autosomal dominant hypercholesterolemia (ADH), and LDLRAP1 responsible for autosomal recessive hypercholesterolemia (ARH). Aim of this study was the review of the clinical and molecular features of patients with HoFH identified in Italy from 1989 to 2019. MethodsData were collected from lipid clinics and laboratories, which had performed molecular diagnosis in suspected HoFH. Clinical data included baseline lipid levels and ASCVD events. ResultsA total of 125 subjects with ADH were identified, of whom 60 were true homozygotes, 58 compound heterozygotes and 7 double heterozygotes for LDLR (likely) pathogenic variants. Compared with compound heterozygotes, true homozygotes showed a more severe lipid phenotype and more ASCVD events. ADH carriers of LDLR negative variants (R-NEG) presented with a more aggressive phenotype, as compared to carriers of LDLR defective variants (R-DEF). Kaplan-Meier analysis showed that the median age of ASCVD event-free survival was 25 years of age in R-NEG as opposed to 50 years of age in R-DEF patients. A total of 66 patients with ARH were also identified, of whom 46 were homozygotes and 20 compound heterozygotes. The phenotypic features of ARH patients were similar to those of R-DEF/ADH patients. Overall, 45% ADH patients and 33% ARH patients did not meet the classic diagnostic criteria for HoFH. ConclusionsIn our cohort, the phenotypic variability of HoFH was dependent on the candidate gene involved and the functional impact of its variants on the LDL receptor pathway.