Contemporary lipid-lowering management and risk of cardiovascular events in homozygous familial hypercholesterolaemia: insights from the Italian LIPIGEN Registry.

AIMS: The availability of novel lipid-lowering therapies (LLTs) has remarkably changed the clinical management of homozygous familial hypercholesterolaemia (HoFH). The impact of these advances was evaluated in a cohort of 139 HoFH patients followed in a real-world clinical setting. METHODS AND RESULTS: The clinical characteristics of 139 HoFH patients, along with information about LLTs and low-density lipoprotein cholesterol (LDL-C) levels at baseline and after a median follow-up of 5 years, were retrospectively retrieved from the records of patients enrolled in the LIPid transport disorders Italian GEnetic Network-Familial Hypercholesterolaemia (LIPIGEN-FH) Registry. The annual rates of major atherosclerotic cardiovascular events (MACE-plus) during follow-up were compared before and after baseline. Additionally, the lifelong survival free from MACE-plus was compared with that of the historical LIPIGEN HoFH cohort. At baseline, LDL-C level was 332 ± 138 mg/dL. During follow-up, the potency of LLTs was enhanced and, at the last visit, 15.8% of patients were taking quadruple therapy. Consistently, LDL-C decreased to an average value of 124 mg/dL corresponding to a 58.3% reduction (Pt < 0.001), with the lowest value (∼90 mg/dL) reached in patients receiving proprotein convertase subtilisin/kexin type 9 inhibitors and lomitapide and/or evinacumab as add-on therapies. The average annual MACE-plus rate in the 5-year follow-up was significantly lower than that observed during the 5 years before baseline visit (21.7 vs. 56.5 per 1000 patients/year; P = 0.0016). CONCLUSION: Our findings indicate that the combination of novel and conventional LLTs significantly improved LDL-C control with a signal of better cardiovascular prognosis in HoFH patients. Overall, these results advocate the use of intensive, multidrug LLTs to effectively manage HoFH.

Contemporary real-world data from the Italian cohort of patients affected by homozygous familial hypercholesterolaemia demonstrated that the addition of novel, low-density lipoprotein receptor (LDLR)-independent medications to conventional therapies allowed the achievement of unprecedented low-density lipoprotein cholesterol (LDL-C) values with a trend towards a reduction of cardiovascular risk.

Clinical Approach in the Management of Paediatric Patients with Familial Hypercholesterolemia: A National Survey Conducted by the LIPIGEN Paediatric Group.

Detection and treatment of patients with familial hypercholesterolemia (FH) starting from childhood is fundamental to reduce morbidity and mortality. The activity of National realities such as the LIPIGEN (LIpid transPort disorders Italian GEnetic Network) Paediatric Group, founded in 2018, is a milestone in this context. The aim of this exploratory survey, conducted in October 2021 among Italian lipid clinics included in the LIPIGEN Paediatric Group, was to investigate the current clinical approach in the management and treatment of paediatric patients with suspected FH. A digital questionnaire composed of 20 questions investigating nutritional treatment and nutraceutical and pharmacological therapy for children and adolescents with FH was proposed to the principal investigators of 30 LIPIGEN centres. Twenty-four centres responded to the section referring to children aged < 10 years and 30 to that referring to adolescents. Overall, 66.7% of children and 73.3% of adolescents were given lipid-lowering nutritional treatment as the first intervention level for at least 3-4 months (29.2% and 23.3%) or 6-12 months (58.3% and 53.3%). Nutraceuticals were considered in 41.7% (regarding children) and 50.0% (regarding adolescents) of the centres as a supplementary approach to diet. Lipid-lowering drug therapy initiation was mainly recommended (91.7% and 80.0%). In 83.3% of children and 96.7% of adolescents, statins were the most frequently prescribed drug. We highlighted several differences in the treatment of paediatric patients with suspected FH among Italian centres; however, the overall approach is in line with the European Atherosclerosis Society (EAS) recommendations for FH children and adolescents. We consider this survey as a starting point to reinforce collaboration between LIPIGEN centres and to elaborate in the near future a consensus document on the management of paediatric patients with suspected FH so as to improve and uniform detection, management, and treatment of these patients in our country.

Lipoprotein(a) Genotype Influences the Clinical Diagnosis of Familial Hypercholesterolemia.

Background Evidence suggests that LPA risk genotypes are a possible contributor to the clinical diagnosis of familial hypercholesterolemia (FH). This study aimed at determining the prevalence of LPA risk variants in adult individuals with FH enrolled in the Italian LIPIGEN (Lipid Transport Disorders Italian Genetic Network) study, with (FH/M+) or without (FH/M-) a causative genetic variant. Methods and Results An lp(a) [lipoprotein(a)] genetic score was calculated by summing the number risk-increasing alleles inherited at rs3798220 and rs10455872 variants. Overall, in the 4.6% of 1695 patients with clinically diagnosed FH, the phenotype was not explained by a monogenic or polygenic cause but by genotype associated with high lp(a) levels. Among 765 subjects with FH/M- and 930 subjects with FH/M+, 133 (17.4%) and 95 (10.2%) were characterized by 1 copy of either rs10455872 or rs3798220 or 2 copies of either rs10455872 or rs3798220 (lp(a) score ≥1). Subjects with FH/M- also had lower mean levels of pretreatment low-density lipoprotein cholesterol than individuals with FH/M+ (t test for difference in means between FH/M- and FH/M+ groups <0.0001); however, subjects with FH/M- and lp(a) score ≥1 had higher mean (SD) pretreatment low-density lipoprotein cholesterol levels (223.47 [50.40] mg/dL) compared with subjects with FH/M- and lp(a) score=0 (219.38 [54.54] mg/dL for), although not statistically significant. The adjustment of low-density lipoprotein cholesterol levels based on lp(a) concentration reduced from 68% to 42% the proportion of subjects with low-density lipoprotein cholesterol level ≥190 mg/dL (or from 68% to 50%, considering a more conservative formula). Conclusions Our study supports the importance of measuring lp(a) to perform the diagnosis of FH appropriately and to exclude that the observed phenotype is driven by elevated levels of lp(a) before performing the genetic test for FH.

Guidance for the diagnosis and treatment of hypolipidemia disorders.

The Abetalipoproteinemia and Related Disorders Foundation was established in 2019 to provide guidance and support for the life-long management of inherited hypocholesterolemia disorders. Our mission is "to improve the lives of individuals and families affected by abetalipoproteinemia and related disorders". This review explains the molecular mechanisms behind the monogenic hypobetalipoproteinemia disorders and details their specific pathophysiology, clinical presentation and management throughout the lifespan. In this review, we focus on abetalipoproteinemia, homozygous hypobetalipoproteinemia and chylomicron retention disease; rare genetic conditions that manifest early in life and cause severe complications without appropriate treatment. Absent to low plasma lipid levels, in particular cholesterol and triglyceride, along with malabsorption of fat and fat-soluble vitamins are characteristic features of these diseases. We summarize the genetic basis of these disorders, provide guidance in their diagnosis and suggest treatment regimens including high dose fat-soluble vitamins as therapeutics. A section on preconception counseling and other special considerations pertaining to pregnancy is included. This information may be useful for patients, caregivers, physicians and insurance agencies involved in the management and support of affected individuals.

Familial chylomicronemia syndrome. A sixty year follow-up in two siblings and their kindreds. Nosological and clinical considerations.

Familial chylomicronemia syndrome (FCS) is a rare and severe genetic disorder, characterized by marked elevation of plasma triglycerides, often diagnosed in infancy. We describe the long-term follow-up (almost 60 years), the diagnostic assessment and the management of two siblings with severe hypertriglyceridemia and a history of pancreatitis who also developed cardiovascular complications later in life. We recently disclosed that the surviving index case was homozygous for a pathogenic LPL gene variant (c.984 G>T, p.M328I). The same variant was also found in two apparently unrelated siblings with FCS living in the same geographical area as the index case.

Lipoprotein(a) and family history for cardiovascular disease in paediatric patients: A new frontier in cardiovascular risk stratification. Data from the LIPIGEN paediatric group.

BACKGROUND AND AIMS: Little is known about the role of Lp(a) in the assessment of cardiovascular risk in the paediatric population. Trying to clarify the clinical relevance of Lp(a) in risk stratification, the aim of the study is to evaluate the association between Lp(a) plasma levels in children with familial hypercholesterolaemia (FH) and positive family history for premature cardiovascular disease (pCVD) in first- and second-degree relatives. METHODS: 653 Caucasian children and adolescents (334 females and 319 males), aged 2-17 years, with diagnosis of FH from a paediatric cohort included in the LIPIGEN Network, were selected. We compared family history of pCVD, lipid and genetic profile in two groups based on Lp(a) levels below or above 30 mg/dL. To determine the independent predictors of pCVD, a multivariate logistic regression was used, with all clinical characteristics and blood measurements as predictors. RESULTS: Subjects with Lp(a) > 30 mg/dl more frequently reported positive family history of pCVD compared to subjects with Lp(a)≤30 mg/dl (69.90% vs 36.66%, p < 0.0001), while did not show differences in terms of median [interquartile range] LDL-cholesterol level (153.00 [88.00 vs 164.50 [90.25] mg/dL, p = 0.3105). In the regression analysis, Lp(a) > 30 mg/dl was an independent predictor of family history of pCVD. Comparing subjects with or without family history of pCVD, we reported significant differences for Lp(a) > 30 mg/dl (46.25% vs 17.65%, p < 0.0001), FH genetic mutation (50.48% vs 40.75%, p = 0,0157), as well as for LDL-cholesterol (p = 0.0013) and total cholesterol (p = 0.0101). CONCLUSIONS: Children/adolescents with FH and Lp(a) > 30 mg/dl where more likely to have a positive family history of pCVD. Lp(a) screening in children and adolescents with FH may enhance risk assessment and help identify those subjects, children and relatives, at increased pCVD risk.

HDL-mediated reduction of cholesterol content inhibits the proliferation of prostate cancer cells induced by LDL: Role of ABCA1 and proteasome inhibition.

High-density lipoproteins (HDL) are well known for their atheroprotective function, mainly due to their ability to remove cell cholesterol and to exert antioxidant and anti-inflammatory activities. Through the same mechanisms HDL could also affect the development and progression of tumors. Cancer cells need cholesterol to proliferate, especially in hormone-dependent tumors, as prostate cancer (PCa). Aim of the study was to investigate the ability of HDL to modulate cholesterol content and metabolism in androgen receptor (AR)-positive and AR-null PCa cell lines and the consequences on cell proliferation. HDL inhibited colony formation of LNCaP and PC3 cells. HDL reduced cell cholesterol content and proliferation of LNCaP cells loaded with low-density lipoproteins but were not effective on PC3 cells. Here, the expression of the ATP-binding cassette transporter A1 (ABCA1) was markedly reduced due to proteasome degradation. Bortezomib, a proteasome inhibitor, restored ABCA1 expression and HDL ability to promote cholesterol removal from PC3; consequently, HDL inhibited the proliferation of PC3 cells induced by LDL only after bortezomib pre-treatment. In conclusion, the antiproliferative activity of HDL on AR-positive and AR-null PCa cells also rely on cholesterol removal, a process in which the ABCA1 transporter plays a key role.

Comparison of two polygenic risk scores to identify non-monogenic primary hypocholesterolemias in a large cohort of Italian hypocholesterolemic subjects.

BACKGROUND: Primary Hypobetalipoproteinemias (HBL) are a group of dominant and recessive monogenic genetic disorders caused by mutations in APOB, PCSK9, ANGPTL3, MTTP, Sar1b genes and characterized by plasma levels of total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C) and apolipoprotein B (apoB) below the 5th percentile of the distribution in a given population. Mutations in the candidate genes account only for a small proportion of subjects with HBL suggesting a role for a polygenic contribution to the low cholesterol phenotype. OBJECTIVE: To explore the complex genetic architecture of HBL we compared two polygenic risk scores in order to assess the role of the polygenic burden and the differences in the clinical phenotype between monogenic and polygenic HBL; we studied a cohort of 170 subjects with primary HBL referred over a 25-year period to 2 Italian reference centers have been studied. METHODS: The genetic analyses have been based on: Sanger sequencing, in-house NGS customized panel and two scores, PRS1 and PRS2 for the polygenic burden. RESULTS: Sixty 60 (35%) and 63 (37%) subjects had a monogenic and polygenic HBL respectively. LDL-C plasma levels were significantly lower in monogenic HBL (30.87 ± 3.12 mg/dl) compared with the non-monogenic HBL (42.80 ± 2.18 mg/dl) (p<0.002) with no differences in the percentage of fatty liver. CONCLUSION: Only PRS1 is effective in detecting polygenic HBL while PRS2 does not improve the polygenic diagnosis.

Homozygous familial hypercholesterolemia in Italy: Clinical and molecular features.

BACKGROUND AND AIMS: Homozygous 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. METHODS: Data were collected from lipid clinics and laboratories, which had performed molecular diagnosis in suspected HoFH. Clinical data included baseline lipid levels and ASCVD events. RESULTS: A 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. CONCLUSIONS: In 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.

In vitro functional characterization of splicing variants of the APOB gene found in familial hypobetalipoproteinemia.

BACKGROUND: Familial hypobetalipoproteinemia type 1 (FHBL-1) is a codominant disorder characterized by greatly reduced plasma levels of total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B. Rare exonic pathogenic variants of APOB gene (nonsense variants, minute deletions/insertions and nonsynonymous variants) have been frequently reported in subjects with FHBL-1. Also, rare intronic variants of APOB located at intron/exon junctions and assumed to affect splicing have been reported. However, the pathogenicity of most of these intronic variants remains to be established. OBJECTIVE: The objective of this study was the in vitro functional characterization of six splicing variants of APOB gene identified in seven putative FHBL-1 heterozygotes. METHODS: ApoB minigenes harboring each variant were expressed in COS-1 cells and their transcripts were sequenced. RESULTS: Four novel variants (c.237+1G>A, c.818+5G>A, c.3000-1G>T, and c.3842+1G>A), predicted in silico to obliterate splice site activity, were found to generate abnormal transcripts. The abnormal transcripts were generated by the activation of cryptic splice sites or exon skipping. All these transcripts harbored a premature termination codon and were predicted to encode truncated apoBs devoid of function. The predicted translation products were: i) p.(Lys41Serfs*2) and p.(Val80Ilefs*10) for c.237+1G>A; ii) p.(Asn274*) for c.818+5G>A; iii) p.(Leu1001Alafs*10) for c.3000-1G>T, and iv) p.(Ser1281Argfs*2) for c.3842+1G>A. Two previously annotated rare variants (c.905-15C>G and c.1618-4G>A) with uncertain effect in silico were found to generate only wild-type transcripts. CONCLUSIONS: These in vitro minigene expression studies support the assignment of pathogenicity to four novel splice site variants of APOB gene found in FHBL-1.

Novel mutations of SAR1B gene in four children with chylomicron retention disease.

BACKGROUND: Intestinal lipid malabsorption, resulting from an impaired formation or secretion of chylomicrons and associated with severe hypobetalipoproteinemia (HBL), may be due to biallelic mutations in APOB (homozygous FHBL type-1), MTTP (abetalipoproteinemia), or SAR1B (chylomicron retention disease). OBJECTIVE: We investigated four children, each born from consanguineous parents, presenting with steatorrhea, malnutrition, accumulation of lipids in enterocytes, and severe hypocholesterolemia with an apparent recessive transmission. METHODS: We sequenced a panel of genes whose variants may be associated with HBL. RESULTS: Case 1, a 9-month-old male, was found to be homozygous for a SAR1B variant (c.49 C>T), predicted to encode a truncated Sar1b protein devoid of function (p.Gln17*). Case 2, a 4-year-old male, was found to be homozygous for a SAR1B missense variant [c.409 G>C, p.(Asp137His)], which affects a highly conserved residue close to the Sar1b guanosine recognition site. Case 3, a 6-year-old male, was found to be homozygous for an ∼6 kb deletion of the SAR1B gene, which eliminates exon 2; this deletion causes the loss of the ATG translation initiation codon in the SAR1B mRNA. The same homozygous mutation was found in an 11-month-old child (case 4) who was related to case 3. CONCLUSIONS: We report 4 children with intestinal lipid malabsorption were found to have chylomicron retention disease due to 3 novel variants in the SAR1B gene.

Angiopoietin-like protein 3 (ANGPTL3) deficiency and familial combined hypolipidemia.

Three members of the angiopoietin-like (ANGPTL) protein family-ANGPTL3, ANGPTL4 and ANGPTL8- are important regulators of plasma lipoproteins. They inhibit the enzyme lipoprotein lipase, which plays a key role in the intravascular lipolysis of triglycerides present in some lipoprotein classes. This review focuses on the role of ANGPTL3 as emerged from the study of genetic variants of Angptl3 gene in mice and humans. Both loss of function genetic variants and inactivation of Angptl3 gene in mice are associated with a marked reduction of plasma levels of triglyceride and cholesterol and an increased activity of lipoprotein lipase and endothelial lipase. In humans with ANGPTL3 deficiency, caused by homozygous loss of function (LOF) variants of Angptl3 gene, the levels of all plasma lipoproteins are greatly reduced. This plasma lipid disorder referred to as familial combined hypolipidemia (FHBL2) does not appear to be associated with distinct pathological manifestations. Heterozygous carriers of LOF variants have reduced plasma levels of total cholesterol and triglycerides and are at lower risk of developing atherosclerotic cardiovascular disease, as compared to non-carriers. These observations have paved the way to the development of strategies to reduce the plasma level of atherogenic lipoproteins in man by the inactivation of ANGPTL3, using either a specific monoclonal antibody or anti-sense oligonucleotides.

Familial hypercholesterolemia: The Italian Atherosclerosis Society Network (LIPIGEN).

BACKGROUND AND AIMS: Primary dyslipidemias are a heterogeneous group of disorders characterized by abnormal levels of circulating lipoproteins. Among them, familial hypercholesterolemia is the most common lipid disorder that predisposes for premature cardiovascular disease. We set up an Italian nationwide network aimed at facilitating the clinical and genetic diagnosis of genetic dyslipidemias named LIPIGEN (LIpid TransPort Disorders Italian GEnetic Network). METHODS: Observational, multicenter, retrospective and prospective study involving about 40 Italian clinical centers. Genetic testing of the appropriate candidate genes at one of six molecular diagnostic laboratories serving as nationwide DNA diagnostic centers. RESULTS AND CONCLUSIONS: From 2012 to October 2016, available biochemical and clinical information of 3480 subjects with familial hypercholesterolemia identified according to the Dutch Lipid Clinic Network (DLCN) score were included in the database and genetic analysis was performed in 97.8% of subjects, with a mutation detection rate of 92.0% in patients with DLCN score ≥6. The establishment of the LIPIGEN network will have important effects on clinical management and it will improve the overall identification and treatment of primary dyslipidemias in Italy.

Spectrum of mutations in Italian patients with familial hypercholesterolemia: New results from the LIPIGEN study.

BACKGROUND: Familial hypercholesterolemia (FH) is an autosomal dominant disease characterized by elevated plasma levels of LDL-cholesterol that confers an increased risk of premature atherosclerotic cardiovascular disease. Early identification and treatment of FH patients can improve prognosis and reduce the burden of cardiovascular mortality. Aim of this study was to perform the mutational analysis of FH patients identified through a collaboration of 20 Lipid Clinics in Italy (LIPIGEN Study). METHODS: We recruited 1592 individuals with a clinical diagnosis of definite or probable FH according to the Dutch Lipid Clinic Network criteria. We performed a parallel sequencing of the major candidate genes for monogenic hypercholesterolemia (LDLR, APOB, PCSK9, APOE, LDLRAP1, STAP1). RESULTS: A total of 213 variants were detected in 1076 subjects. About 90% of them had a pathogenic or likely pathogenic variants. More than 94% of patients carried pathogenic variants in LDLR gene, 27 of which were novel. Pathogenic variants in APOB and PCSK9 were exceedingly rare. We found 4 true homozygotes and 5 putative compound heterozygotes for pathogenic variants in LDLR gene, as well as 5 double heterozygotes for LDLR/APOB pathogenic variants. Two patients were homozygous for pathogenic variants in LDLRAP1 gene resulting in autosomal recessive hypercholesterolemia. One patient was found to be heterozygous for the ApoE variant p.(Leu167del), known to confer an FH phenotype. CONCLUSIONS: This study shows the molecular characteristics of the FH patients identified in Italy over the last two years. Full phenotypic characterization of these patients and cascade screening of family members is now in progress.

Incidental finding of severe hypertriglyceridemia in children. Role of multiple rare variants in genes affecting plasma triglyceride.

BACKGROUND: The incidental finding of severe hypertriglyceridemia (HyperTG) in a child may suggest the diagnosis of familial chylomicronemia syndrome (FCS), a recessive disorder of the intravascular hydrolysis of triglyceride (TG)-rich lipoproteins. FCS may be due to pathogenic variants in lipoprotein lipase (LPL), as well as in other proteins, such as apolipoprotein C-II and apolipoprotein A-V (activators of LPL), GPIHBP1 (the molecular platform required for LPL activity on endothelial surface) and LMF1 (a factor required for intracellular formation of active LPL). OBJECTIVE: Molecular characterization of 5 subjects in whom HyperTG was an incidental finding during infancy/childhood. METHODS: We performed the parallel sequencing of 20 plasma TG-related genes. RESULTS: Three children with severe HyperTG were found to be compound heterozygous for rare pathogenic LPL variants (2 nonsense, 3 missense, and 1 splicing variant). Another child was found to be homozygous for a nonsense variant of APOA5, which was also found in homozygous state in his father with longstanding HyperTG. The fifth patient with a less severe HyperTG was found to be heterozygous for a frameshift variant in LIPC resulting in a truncated Hepatic Lipase. In addition, 1 of the patients with LPL deficiency and the patient with APOA-V deficiency were also heterozygous carriers of a pathogenic variant in LIPC and LPL gene, respectively, whereas the patient with LIPC variant was also a carrier of a rare APOB missense variant. CONCLUSIONS: Targeted parallel sequencing of TG-related genes is recommended to define the molecular defect in children presenting with an incidental finding of HyperTG.

Clinical and biochemical characteristics of individuals with low cholesterol syndromes: A comparison between familial hypobetalipoproteinemia and familial combined hypolipidemia.

BACKGROUND: The most frequent monogenic causes of low plasma cholesterol are familial hypobetalipoproteinemia (FHBL1) because of truncating mutations in apolipoprotein B coding gene (APOB) and familial combined hypolipidemia (FHBL2) due to loss-of-function mutations in ANGPTL3 gene. OBJECTIVE: A direct comparison of lipid phenotypes of these 2 conditions has never been carried out. In addition, although an increased prevalence of liver steatosis in FHBL1 has been consistently reported, the hepatic consequences of FHBL2 are not well established. METHODS: We investigated 350 subjects, 67 heterozygous carriers of APOB mutations, 63 carriers of the p.S17* mutation in ANGPTL3 (57 heterozygotes and 6 homozygotes), and 220 noncarrier normolipemic controls. Prevalence and degree of hepatic steatosis were assessed by ultrasonography. RESULTS: A steady decrease of low-density lipoprotein cholesterol levels were observed from heterozygous to homozygous FHBL2 and to FHBL1 individuals, with the lowest levels in heterozygous FHBL1 carrying truncating mutations in exons 1 to 25 of APOB (P for trend <.001). Plasma triglycerides levels were similar in heterozygous FHBL1 and homozygous FHBL2 individuals, but higher in heterozygous FHBL2. The lowest high-density lipoprotein cholesterol levels were detected in homozygous FHBL2 (P for trend <.001). Compared with controls, prevalence and severity of hepatic steatosis were increased in heterozygous FHBL1 (P < .001), but unchanged in FHBL2 individuals. CONCLUSION: Truncating APOB mutations showed the more striking low-density lipoprotein cholesterol lowering effect compared with p.S17* mutation in ANGPTL3. Reduced high-density lipoprotein cholesterol levels were the unique lipid characteristic associated with FHBL2. Mutations impairing liver synthesis or secretion of apolipoprotein B are crucial to increase the risk of liver steatosis.

Threshold Effects of Circulating Angiopoietin-Like 3 Levels on Plasma Lipoproteins.

Context: Angiopoietin-like 3 (ANGPTL3) deficiency in plasma due to loss-of-function gene mutations results in familial combined hypobetalipoproteinemia type 2 (FHBL2) in homozygotes. However, the lipid phenotype in heterozygotes is much milder and does not appear to relate directly to ANGPTL3 levels. Furthermore, the low-density lipoprotein (LDL) phenotype in carriers of ANGPTL3 mutations is unexplained. Objective: To determine whether reduction below a critical threshold in plasma ANGPTL3 levels is a determinant of lipoprotein metabolism in FHBL2, and to determine whether proprotein convertase subtilisin kexin type 9 (PCSK9) is involved in determining low LDL levels in this condition. Design: We studied subjects from 19 families with ANGPTL3 mutations and subjects with familial combined hypobetalipoproteinemia type 1 (FHBL1) due to truncated apolipoprotein B (apoB) species. Results: First, total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, and HDL and LDL particle concentration correlated with plasma ANGPTL3 levels but only when the latter was <25% of normal (<60 ng/dL). Second, the very low-density lipoprotein particle concentration correlated strongly with plasma ANGPTL3 when the latter was <58% of normal. Third, both FHBL1 and FHBL2 subjects showed low levels of mature and LDL-bound PCSK9 and higher levels of its furin-cleaved form. Finally, LDL-bound PCSK9 is protected from cleavage by furin and binds to the LDL receptor more strongly than apoB-free PCSK9. Conclusions: Our results suggest that the hypolipidemic effects of ANGPTL3 mutations in FHBL2 are dependent on a threshold of plasma ANGPTL3 levels, with differential effects on various lipoprotein particles. The increased inactivation of PCSK9 by furin in FHBL1 and FHBL2 is likely to cause increased LDL clearance and suggests novel therapeutic avenues.

Impact of rare variants in autosomal dominant hypercholesterolemia causing genes.

PURPOSE OF REVIEW: The systematic analysis of the major candidate genes in autosomal dominant hypercholesterolemia (ADH) and the use of next-generation sequencing (NGS) technology have made possible the discovery of several rare gene variants whose pathogenic effect in most cases remains poorly defined. RECENT FINDINGS: One major advance in the field has been the adoption of a set of international guidelines for the assignment of pathogenicity to low-density lipoprotein receptor (LDLR) gene variants based on the use of softwares, complemented with data available from literature and public databases. The clinical impact of several novel rare variants in LDLR, APOB, PCSK9, APOE genes have been reported in large studies describing patients with ADH found to be homozygotes/compound heterozygotes, double heterozygotes, or simple heterozygotes. In-vitro functional studies have been conducted to clarify the effect of some rare ApoB variants on LDL binding to LDLR and the impact of a rare ApoE variant on the uptake of VLDL and LDL by hepatocytes. SUMMARY: The update of the ADH gene variants database and the classification of variants in categories of pathogenicity is a major advance in the understanding the pathophysiology of ADH and in the management of this disorder. The studies of molecularly characterized patients with ADH have emphasized the impact of a specific variant and the variable clinical expression of different genotypes. The functional studies of some variants have increased our understanding of the molecular bases of some forms of ADH.

Association between familial hypobetalipoproteinemia and the risk of diabetes. Is this the other side of the cholesterol-diabetes connection? A systematic review of literature.

Statin therapy is beneficial in reducing LDL cholesterol (LDL-C) levels and cardiovascular events, but it is associated with the risk of incident diabetes mellitus (DM). Familial hypercholesterolemia (FH) is characterized by genetically determined high levels of plasma LDL-C and a low prevalence of DM. LDL-C levels seem then inversely correlated with prevalence of DM. Familial hypobetalipoproteinemia (FHBL) represents the genetic mirror of FH in terms of LDL-C levels, very low in subjects carrying mutations of APOB, PCSK9 (FHBL1) or ANGPTL3 (FHBL2). This review explores the hypothesis that FHBL might represent also the genetic mirror of FH in terms of prevalence of DM and that it is expected to be increased in FHBL in comparison with the general population. A systematic review of published literature on FHBL was made by searching PubMed (1980-2016) for articles presenting clinical data on FHBL probands and relatives. The standardized prevalence rates of DM in FHBL1 were similar to those of the reference population, with a prevalence rate of 8.2 and 9.2%, respectively, while FHBL2 showed a 4.9% prevalence of DM. In conclusion, low LDL-C levels of FHBL do not seem connected to DM as it happens in subjects undergoing statin therapy and the diabetogenic effect of statins has to be explained by mechanisms that do not rely exclusively on the reduced levels of LDL-C. The review also summarizes the published data on the effects of FHBL on insulin sensitivity and the relationships between FH, statin therapy, FHBL1 and intracellular cholesterol metabolism, evaluating possible diabetogenic pathways.

Clinical and genetic features of 3 patients with familial chylomicronemia due to mutations in GPIHBP1 gene.

BACKGROUND: Familial chylomicronemia is a recessive disorder that may be due to mutations in lipoprotein lipase (LPL) and in other proteins such as apolipoprotein C-II and apolipoprotein A-V (activators of LPL), GPIHBP1 (the molecular platform required for LPL activity on endothelial surface), and LMF1 (a factor required for intracellular formation of active LPL). METHODS: We sequenced the familial chylomicronemia candidate genes in 2 adult females presenting long-standing hypertriglyceridemia and a history of acute pancreatitis. RESULTS: Both probands had plasma triglyceride >10 mmol/L but no mutations in the LPL gene. The sequence of the other candidate genes showed that one patient was homozygous for a novel missense mutation p.(Cys83Arg), and the other was homozygous for a previously reported nonsense mutation p.(Cys 89*), respectively, in GPIHBP1. Family screening showed that the hypertriglyceridemic brother of the p.(Cys83Arg) homozygote was also homozygous for this mutation. He had no history of pancreatitis. The p.(Cys83Arg) heterozygous carriers had normal triglyceride levels. The substitution of a cysteine residue in the Ly6 domain of GPIHBP1 is predicted to abolish one of the disulfide bridges required to maintain the structure of GPIHBP1. The p.(Cys89*) mutation results in a truncated protein devoid of function. CONCLUSIONS: Both mutant GPIHBP1 proteins are expected to be incapable of transferring LPL from the subendothelial space to the endothelial surface.