Characterization of a mutant form of human apolipoprotein B (Thr26_Tyr27del) associated with familial hypobetalipoproteinemia

We have previously identified a deletion mutant of human apoB [apoB (Thr26_Tyr27del)] in a subject with primary hypobetalipoproteinemia. The present study determined the effect of Thr26_Tyr27del mutation on apoB secretion using transfected McA-RH7777 cells. Transient or stable transfection of apoB-48 containing the Thr26_Tyr27del mutation showed drastically reduced secretion of the mutant as compared to wild-type apoB-48. No lipoproteins containing the mutant apoB-48 were secreted into the medium. Incubation of transfected cells in a lipid-rich medium in the presence of cycloheximide showed rapid turnover of cell-associated mutant apoB-48 as compared to that of wild-type apoB-48. Immunofluo…

Familial HDL deficiency due to ABCA1 gene mutations with or without other genetic lipoprotein disorders

Mutations in ABCA1 have been shown to be the cause of Tangier disease (TD) and some forms of familial hypoalphalipoproteinemia (HA), two genetic disorders characterized by low plasma HDL levels. Here we report six subjects with low HDL, carrying seven ABCA1 mutations, six of which are previously unreported. Two mutations (R557X and H160FsX173) were predicted to generate short truncated proteins; two mutations (E284K and Y482C) were located in the first extracellular loop and two (R1901S and Q2196H) in the C-terminal cytoplasmic domain of ABCA1. Two subjects found to be compound heterozygotes for ABCA1 mutations did not have overt clinical manifestations of TD. Three subjects, all with prema…

Additive effect of mutations in LDLR and PCSK9 genes on the phenotype of familial hypercholesterolemia.

Patients homozygous or Compound heterozygous for LDLR mutations or double heterozygous for LDLR and apo B R3500Q mutation have higher LDL-C levels. more extensive xanthomatosis and more severe premature coronary disease (pCAD) than simple heterozygotes for mutations in either these genes or for missense mutations in PCSK9 gene. It is not known whether combined mutations in LDLR and PKCS9 are associated with such a severe phenotype. We sequenced Apo B and PCSK9 genes in two patients with the clinical diagnosis of homozygous FH who were heterozygous for LDLR gene mutations. Proband Z.P. (LDL-C 13.39 mmol/L and pCAD) was heterozygous for an LDLR mutation (p.E228K) inherited from her father (LD…

Homozygous familial hypercholesterolemia in Italy: Clinical and molecular features

Abstract 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, …

Molecular diagnosis of hypobetalipoproteinemia: an ENID review.

Abstract Primary hypobetalipoproteinemia (HBL) includes a group of genetic disorders: abetalipoproteinemia (ABL) and chylomicron retention disease (CRD), with a recessive transmission, and familial hypobetalipoproteinemia (FHBL) with a co-dominant transmission. ABL and CRD are rare disorders due to mutations in the MTP and SARA2 genes, respectively. Heterozygous FHBL is much more frequent. FHBL subjects often have fatty liver and, less frequently, intestinal fat malabsorption. FHBL may be linked or not to the APOB gene. Most mutations in APOB gene cause the formation of truncated forms of apoB which may or may be not secreted into the plasma. Truncated apoBs with a size below that of apoB-3…

Spectrum of mutations of the LPL gene identified in Italy in patients with severe hypertriglyceridemia.

Background: Monogenic hypertriglyceridemia (HTG) may result from mutations in some genes which impair the intravascular lipolysis of triglyceride (TG)-rich lipoproteins mediated by the enzyme Lipoprotein lipase (LPL). Mutations in the LPL gene are the most frequent cause of monogenic HTG (familial chylomicronemia) with recessive transmission. Methods: The LPL gene was resequenced in 149 patients with severe HTG (TG>10mmol/L) and 106 patients with moderate HTG (TG>4.5 and <10mmol/L) referred to tertiary Lipid Clinics in Italy. Results: In the group of severe HTG, 26 patients (17.4%) were homozygotes, 9 patients (6%) were compound heterozygotes and 15 patients (10%) were simple heter…

Overview of the current status of familial hypercholesterolaemia care in over 60 countries - The EAS Familial Hypercholesterolaemia Studies Collaboration (FHSC)

PubMed: 30270054

Identifying genetic risk variants for coronary heart disease in familial hypercholesterolemia: an extreme genetics approach

Mutations in the low-density lipoprotein receptor (LDLR) gene cause familial hypercholesterolemia (FH), a disorder characterized by coronary heart disease (CHD) at young age. We aimed to apply an extreme sampling method to enhance the statistical power to identify novel genetic risk variants for CHD in individuals with FH. We selected cases and controls with an extreme contrast in CHD risk from 17 000 FH patients from the Netherlands, whose functional LDLR mutation was unequivocally established. The genome-wide association (GWA) study was performed on 249 very young FH cases with CHD and 217 old FH controls without CHD (above 65 years for males and 70 years of age for females) using the Ill…

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 …

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

Abstract 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…

Corrigendum to "Molecular diagnosis of hypobetalipoproteinemia: An ENID review" [Atherosclerosis 195 (2) (2007) 19-27].

Familial combined hypolipidemia due to mutations in the ANGPTL3 gene

The role of ANGPTL3 in lipoprotein metabolism emerged from studies in a mutant mouse strain characterized by severe hypotriglyceridemia and carrying a loss-of-function (LOF) mutation of the ANGPTL3 gene. ANGPTL3 was found to inhibit lipoprotein lipase and endothelial lipase. Genome-wide association studies in humans demonstrated the association of ANGPTL3 variants with plasma triglyceride levels and LOF mutations of ANGPTL3 were found in hypotriglyceridemic subjects in population studies. Recently, individuals originally classified as affected by familial hypobetalipoproteinemia were found to be homozygotes/compound heterozygotes for rare LOF mutations of ANGPTL3. They show a striking reduc…

Genetic polymorphisms affecting the phenotypic expression in familial hypercholesterolemia

The clinical expression of heterozygous familial hypercholesterolemia (FH) is highly variable even in patients carrying the same LDL receptor (LDL-R) gene mutation. This variability might be due to environmental factors as well as to modifying genes affecting lipoprotein metabolism. We investigated Apo E (2, 3, 4), MTP (-493G/T), Apo B (-516C/T), Apo A-V (-1131T/C), HL (-514C/T and -250G/A), FABP-2 (A54T), LPL (D9N, N291S, S447X) and ABCA1 (R219K) polymorphisms in 221 unrelated FH index cases and 349 FH relatives with defined LDL-R gene mutations. We found a significant and independent effect of the following polymorphisms on: (i) plasma LDL-C (Apo E, MTP and Apo B); (ii) plasma HDL-C (HL, …

Mutations in MTP gene in abeta- and hypobeta-lipoproteinemia.

Abstract Familial hypobetalipoproteinemia (FHBL) and abetalipoproteinemia (ABL) are inherited disorders of apolipoprotein B (apo B)-containing lipoproteins that result from mutations in apo B and microsomal triglyceride transfer protein (MTP) genes, respectively. Here we report three patients with severe deficiency of plasma low-density lipoprotein (LDL) and apo B. Two of them (probands F.A. and P.E.) had clinical and biochemical phenotype consistent with ABL. Proband F.A. was homozygous for a minute deletion/insertion (c.1228delCCCinsT) in exon 9 of MTP gene predicted to cause a truncated MTP protein of 412 amino acids. Proband P. E. was heterozygous for a mutation in intron 9 (IVS9-1G>A),…

CLINICAL CHARACTERISTICS AND PLASMA LIPIDS IN SUBJECTS WITH FAMILIAL COMBINED HYPOLIPIDEMIA: A POOLED ANALYSIS

Background. Angiopoietin-like 3 (ANGPTL3) regulates lipoprotein metabolism by modulating extracellular lipases. Loss-of function mutations in ANGPTL3 gene cause familial combined hypolipidemia (FHBL2). The mode of inheritance and hepatic and vascular consequences of FHBL2 have not been fully elucidated. To get further insights on these aspects, we re-evaluated the clinical and the biochemical characteristics of all reported cases of FHBL2. Methods and Results. One hundred fteen FHBL2 individuals carrying 13 different mutations in the ANGPTL3 gene (14 homozygotes, 8 compound heterozygotes and 93 heterozygotes) and 402 controls were considered. Carriers of 2 mutant alleles had undetectable pl…

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 nationw…

Worldwide experience of homozygous familial hypercholesterolaemia:retrospective cohort study

[Background]: Homozygous familial hypercholesterolaemia (HoFH) is a rare inherited disorder resulting in extremely elevated low-density lipoprotein cholesterol levels and premature atherosclerotic cardiovascular disease (ASCVD). Current guidance about its management and prognosis stems from small studies, mostly from high-income countries. The objective of this study was to assess the clinical and genetic characteristics, as well as the impact, of current practice on health outcomes of HoFH patients globally.

Spectrum of mutations and phenotypic expression in patients with autosomal dominant hypercholesterolemia identified in Italy.

Abstract Objective To determine the spectrum of gene mutations and the genotype–phenotype correlations in patients with Autosomal Dominant Hypercholesterolemia (ADH) identified in Italy. Methods The resequencing of LDLR , PCSK9 genes and a selected region of APOB gene were conducted in 1018 index subjects clinically heterozygous ADH and in 52 patients clinically homozygous ADH. The analysis was also extended to 1008 family members of mutation positive subjects. Results Mutations were detected in 832 individuals: 97.4% with LDLR mutations, 2.2% with APOB mutations and 0.36% with PCSK9 mutations. Among the patients with homozygous ADH, 51 were carriers of LDLR mutations and one was an LDLR / …