Browsing by Author "Martin, Cesar"
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- Characterization of the First PCSK9 Gain of Function HomozygotePublication . Alves, Ana Catarina; Etxebarria, Aitor; Medeiros, Ana Margarida; Benito-Vicente, Asier; Thedrez, Aurélie; Passard, Maxime; Croyal, Mikaël; Martin, Cesar; Lambert, Gilles; Bourbon, MafaldaGain of function (GOF) mutations in proprotein convertase subtilisin kexin type 9 (PCSK9) are a rare cause of familial hypercholesterolemia (FH). We identified a child with a clinical diagnosis of FH with 2 novel putative PCSK9 GOF missense variants (p.[(Ala62Asp)]; [(Pro467Ala)]), and no mutation in the low-density lipoprotein (LDL) receptor (LDLR) or in apolipoprotein B100 (APOB) genes. The proband was referred to the Portuguese FH Study (1) at age 11 and presented a total cholesterol of 316 mg/dl and low-density lipoprotein cholesterol (LDL-C) of 234 mg/dl on a strict diet. The phenotype presented by all PCSK9 heterozygous carriers within this large pedigree is similar to APOB heterozygous carriers (LDL-C, 198.75 ± 14.98 mg/dl vs. LDL-C, 211.57 ± 42.02 mg/dl; p = 0.227) but significantly different than heterozygous LDLR carriers (LDL-C, 198.75 ± 14.98 mg/dl vs. LDL-C, 230.63 ± 76.50 mg/dl; p = 0.012) when comparing the relatives’ phenotype in our cohort.
- Functional Analysis of LDLR (Low-Density Lipoprotein Receptor) Variants in Patient Lymphocytes to Assess the Effect of Evinacumab in Homozygous Familial Hypercholesterolemia Patients With a Spectrum of LDLR ActivityPublication . Banerjee, Poulabi; Chan, Kuo-Chen; Tarabocchia, Michel; Benito-Vicente, Asier; Alves, Ana C.; Uribe, Kepa B.; Bourbon, Mafalda; Skiba, Paul J.; Pordy, Robert; Gipe, Daniel A.; Gaudet, Daniel; Martin, CesarOBJECTIVE: Homozygous familial hypercholesterolemia is a rare disease usually caused by LDLR (low-density lipoprotein receptor) mutations. Homozygous familial hypercholesterolemia is characterized by markedly elevated LDL-C (low-density lipoprotein cholesterol) levels and an extremely high risk of premature atherosclerotic cardiovascular disease. A phase 2, proof-of-concept study (NCT02265952) demonstrated that evinacumab, a fully human monoclonal antibody to ANGPTL3 (angiopoietin-like 3 protein), reduced LDL-C levels in 9 patients with genotypically confirmed homozygous familial hypercholesterolemia and was well tolerated. The aim of this study was to analyze the effects of evinacumab on LDLR activity in lymphocytes purified from patients in the proof-of-concept study. APPROACH AND RESULTS: LDLR activity was assessed in patient lymphocytes before and after treatment with evinacumab and versus lymphocytes carrying wild-type LDLR, and also in an LDLR-defective Chinese hamster ovary cell line (CHO-ldlA7) transfected with plasmids encoding the LDLR variants. Overall mean peak reduction in LDL-C with evinacumab was −58±18%, occurring between Week 4 and Week 12. Mutations identified in the 9 patients were shown to be pathogenic, with loss of LDLR activity versus wild type. Two of the LDLR variants, p.(Cys681*) and p.(Ala627Profs*38), were class 2 type mutations that are retained in the endoplasmic reticulum. Six variants were class 3 type mutations with impaired LDL-C binding activity: p.(Trp87Gly), occurring in 2 patients, p.(Gln254Pro), p.(Ser177Leu), p.(Gly335Val), and p.(Ser306Leu). Evinacumab had no effect on LDLR activity. CONCLUSIONS: These results suggest that evinacumab is effective for lowering LDL-C in patients with homozygous familial hypercholesterolemia, and the inhibition of ANGPTL3 in humans lowers LDL-C in a mechanism independent of the LDLR.
- Further evidence of novel APOB mutations as a cause of familial hypercholesterolaemiaPublication . Alves, Ana Catarina; Benito-Vicente, Asier; Medeiros, Ana Margarida; Reeves, Kaajal; Martin, Cesar; Bourbon, MafaldaAPOB mutations are a rare cause of familial hypercholesterolaemia (FH) and, until recently, routine genetic diagnosis only included the study of two small APOB fragments. In previous years, 5 novel functional mutations have been described in APOB fragments not routinely studied, our group having functionally characterized 2 of them. The main aim of this work was to identify and characterize novel alterations in APOB to assess the genetic cause of hypercholesterolemia in patients with a clinical diagnosis of FH.
- LDLR variants functional characterization: Contribution to variant classificationPublication . Alves, Ana Catarina; Azevedo, Sílvia; Benito-Vicente, Asier; Graça, Rafael; Galicia-Garcia, Unai; Barros, Patrícia; Jordan, Peter; Martin, Cesar; Bourbon, MafaldaBackground and aims: Familial hypercholesterolaemia (FH) is an autosomal disorder of lipid metabolism presenting with increased cardiovascular risk. LDLR mutations are the cause of disease in 90% of the cases but functional studies have only been performed for about 15% of all LDLR variants. In the Portuguese Familial Hypercholesterolemia Study (PFHS), 142 unique LDLR alterations were identified and 44 (30%) lack functional characterization. The aim of the present work is to increase evidence for variant classification by performing functional characterization of 13 LDLR missense alterations found in Portugal and in 20 other countries. Methods: Different LDLR mutants were generated by site-directed mutagenesis and expressed in CHO-ldlA7 cells lacking endogenous expression of LDLR. To determine the effects of alterations on LDLR function, cell surface expression, binding and uptake of FITC-LDL were assessed by flow cytometry and Western blot. Results: Of the 13 variants studied 7 were shown to affect LDLR function - expression, binding or uptake, with rates lower than 60%: p.(Cys184Tyr), p.(Gly207_Ser213del); p.(His211Asp); p.(Asp221Tyr); p.(Glu288Lys); p.(Gly592Glu) and p.(Asp601Val)). The remaining 6 variants do not alter the LDLR function. Conclusions: These studies contributed to an update of these variants classification: from the 9 variants classified as variants of unknown significance, 7 have reached now a final classification and 3 variants have improved classification from likely pathogenic to pathogenic. In Portugal, an additional 55 patients received an FH definite diagnosis thanks to these studies. Since only likely pathogenic and pathogenic variants are clinically actionable, this work shows the importance of functional studies for variant classification.
- Novel functional APOB mutations outside LDL-binding region causing familial hypercholesterolaemiaPublication . Alves, Ana Catarina; Etxebarria, Aitor; Soutar, Anne Katherine; Martin, Cesar; Bourbon, Mafalda
- Novel functional APOB mutations outside LDL-binding region causing familial hypercholesterolaemiaPublication . Alves, Ana Catarina; Etxebarria, Aitor; Soutar, Anne Katherine; Martin, Cesar; Bourbon, MafaldaFamilial hypercholesterolaemia (FH) is characterized by increased circulating low-density lipoprotein (LDL) cholesterol leading to premature atherosclerosis and coronary heart disease. Although FH is usually caused by mutations in LDLR, mutations in APOB and PCSK9 also cause FH but only a few mutations have been reported, APOB p.R3527Q being the most common. However, 30-80% of clinical FH patients do not present an identifiable mutation in any of the described genes. To identify the genetic cause of the hypercholesterolaemia in 65 patients without mutations in LDLR, PCSK9 or in fragments of exon 26 and 29 of APOB currently analysed, we performed whole sequencing of APOB by pyrosequencing. A total of 10 putative mutations in APOB were identified. Flow cytometry with fluorescently labelled LDL from patients and relatives showed that p.Arg1164Thr (exon 22) and p.Gln4494del (exon 29) presented a 40% decrease in internalization in lymphocytes and HepG2 cells, very similar to APOB3527. The proliferation assays with U937 cells showed reduced growth for both cases. The variant p.Tyr1247Cys was found to be neutral and other three alterations were considered polymorphisms. Our results emphasize the need to study the whole APOB in routine protocols to improve patient identification and cardiovascular risk assessment.