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Sniderman AD, Glavinovic T, Thanassoulis G. Key Questions About Familial Hypercholesterolemia: JACC Review Topic of the Week. J Am Coll Cardiol 2022; 79:1023-1031. [PMID: 35272797 DOI: 10.1016/j.jacc.2022.01.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 01/06/2022] [Accepted: 01/07/2022] [Indexed: 12/16/2022]
Abstract
Familial hypercholesterolemia (FH) is characterized as a monogenic, autosomal dominant disorder, producing severe hypercholesterolemia within families due to causal variants within genes regulating the low-density lipoprotein receptor pathway. Demonstration of a causal variant is widely accepted as evidence of substantially higher cardiovascular risk. However, recent large-scale population studies challenge this characterization of FH, which appears to account for only a minor portion of those with severe hypercholesterolemia. Moreover, a substantial portion of FH variant positive patients do not have marked hypercholesterolemia. These discordances raise doubt as to how FH should be defined and how the concentration of low-density lipoprotein in plasma is regulated in individuals with and without FH. Moreover, review of the evidence suggests the impact of an FH causal variant on cardiovascular risk may be less than previously accepted and that all patients with severe hypercholesterolemia should be prioritized for therapy and family screening.
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Affiliation(s)
- Allan D Sniderman
- Mike and Valeria Rosenbloom Centre for Cardiovascular Prevention, Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada.
| | - Tamara Glavinovic
- Division of Nephrology, Department of Medicine, Western University, London, Ontario, Canada
| | - George Thanassoulis
- Mike and Valeria Rosenbloom Centre for Cardiovascular Prevention, Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada. https://twitter.com/thanassoulisMD
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2
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Winther M, Shpitzen S, Yaacov O, Landau J, Oren L, Foroozan-Rosenberg L, Lev Cohain N, Schurr D, Meiner V, Szalat A, Carmi S, Hayden MR, Leitersdorf E, Durst R. In search of a genetic explanation for LDLc variability in an FH family: common SNPs and a rare mutation in MTTP explain only part of LDL variability in an FH family. J Lipid Res 2019; 60:1733-1740. [PMID: 31387896 DOI: 10.1194/jlr.m092049] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2018] [Revised: 06/21/2019] [Indexed: 01/06/2023] Open
Abstract
We previously identified a highly consanguineous familial hypercholesterolemia (FH) family demonstrating segregation of the JD Bari mutation in the LDL receptor as well as a putative cholesterol-lowering trait. We aimed to identify genes related to the latter effect. LDL cholesterol (LDLc) values were normalized for FH affectation status, age, and gender. Using genome-wide SNP data, we examined whether known SNPs gleaned from a genome-wide association study could explain the variation observed in LDLc. Four individuals with markedly reduced LDL levels underwent whole exome sequencing. After prioritizing all potential mutations, we identified the most promising candidate genes and tested them for segregation with the lowering trait. We transfected a plasmid carrying the top candidate mutation, microsomal triglyceride transfer protein (MTTP) R634C, into COS-7 cells to test enzymatic activity. The SNP score explained 3% of the observed variability. MTTP R634C showed reduced activity (49.1 nmol/ml) compared with the WT allele (185.8 nmol/ml) (P = 0.0012) and was marginally associated with reduced LDLc in FH patients (P = 0.05). Phenotypic variability in a FH pedigree can only partially be explained by a combination of common SNPs and a rare mutation and a rare variant in the MTTP gene. LDLc variability in FH patients may have nongenetic causes.
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Affiliation(s)
- Michael Winther
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Shoshi Shpitzen
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Or Yaacov
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.,Hebrew University-Hadassah Braun School of Public Health and Community Medicine, Jerusalem, Israel
| | - Jakob Landau
- Hebrew University-Hadassah Braun School of Public Health and Community Medicine, Jerusalem, Israel
| | - Limor Oren
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Linda Foroozan-Rosenberg
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Naama Lev Cohain
- Radiology Department, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Daniel Schurr
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Vardiela Meiner
- Department of Genetics and Metabolic Diseases, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Auryan Szalat
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.,Internal Medicine Ward, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Shai Carmi
- Hebrew University-Hadassah Braun School of Public Health and Community Medicine, Jerusalem, Israel
| | - Michael R Hayden
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Eran Leitersdorf
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Ronen Durst
- Center for Research, Prevention, and Treatment of Atherosclerosis, Hadassah-Hebrew University Medical Center, Jerusalem, Israel .,Cardiology Division, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
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3
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Huijgen R, Sjouke B, Vis K, de Randamie JSE, Defesche JC, Kastelein JJP, Hovingh GK, Fouchier SW. Genetic variation in APOB, PCSK9, and ANGPTL3 in carriers of pathogenic autosomal dominant hypercholesterolemic mutations with unexpected low LDL-Cl Levels. Hum Mutat 2011; 33:448-55. [PMID: 22095935 DOI: 10.1002/humu.21660] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Accepted: 11/09/2011] [Indexed: 11/11/2022]
Abstract
Autosomal Dominant Hypercholesterolemia (ADH) is caused by LDLR and APOB mutations. However, genetically diagnosed ADH patients do not always exhibit the expected hypercholesterolemic phenotype. Of 4,669 genetically diagnosed ADH patients, identified through the national identification screening program for ADH, 75 patients (1.6%) had LDL-cholesterol (LDL-C) levels below the 50th percentile for age and gender prior to lipid-lowering therapy. The genes encoding APOB, PCSK9, and ANGPTL3 were sequenced in these subjects to address whether monogenic dominant loss-of-function mutations underlie this paradoxical phenotype. APOB mutations, resulting in truncated APOB, were found in five (6.7%) probands, reducing LDL-C by 56%. Rare variants in PCSK9, and ANGPTL3 completely correcting the hypercholesterolemic phenotype were not found. The common variants p.N902N, c.3842+82T>A, p.D2312D, and p.E4181K in APOB, and c.1863+94A>G in PCSK9 were significantly more prevalent in our cohort compared to the general European population. Interestingly, 40% of our probands carried at least one minor allele for all four common APOB variants compared to 1.5% in the general European population. While we found a low prevalence of rare variants in our cohort, our data suggest that regions in proximity of the analyzed loci, and linked to specific common haplotypes, might harbor additional variants that correct an ADH phenotype.
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Affiliation(s)
- Roeland Huijgen
- Department of Vascular Medicine, Academic Medical Center at the University of Amsterdam, Amsterdam, The Netherlands
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4
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Marques-Pinheiro A, Marduel M, Rabès JP, Devillers M, Villéger L, Allard D, Weissenbach J, Guerin M, Zair Y, Erlich D, Junien C, Munnich A, Krempf M, Abifadel M, Jaïs JP, Boileau C, Varret M. A fourth locus for autosomal dominant hypercholesterolemia maps at 16q22.1. Eur J Hum Genet 2010; 18:1236-42. [PMID: 20571503 DOI: 10.1038/ejhg.2010.94] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Autosomal dominant hypercholesterolemia (ADH) is characterized by isolated increase in plasmatic low-density lipoprotein (LDL) cholesterol levels associated with high risk of premature cardiovascular disease. Mutations in LDLR, APOB, and PCSK9 genes have been shown to cause ADH. We now report further genetic heterogeneity of ADH through the study of a large French family in which the involvement of these three genes was excluded. A genome-wide scan mapped the disease-causing gene, named HCHOLA4, at 16q22.1 in a 7.89-Mb interval containing 154 genes with a maximum LOD score of 3.9. To reduce the linked region, we genotyped 18 smaller non-LDLR/non-APOB/non-PCSK9-ADH families at the HCHOLA4 locus. Six families did not exclude linkage to the locus, but none allowed reduction of the disease interval. The 154 regional genes were sorted according to the function of the encoded protein and tissue expression profiles, and 57 genes were analyzed through sequencing of their coding region and close flanking intronic parts. No disease-causing mutation was identified in these families, particularly in the LCAT gene. Finally, our results also show the existence of other ADH genes as nine families were neither linked to LDLR, APOB, and PCSK9 genes nor to the new HCHOLA4 locus.
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Ait Chihab K, Chater R, Cenarro A, Kettani A, Castillo S, Loutfi M, Ribalta J, Adlouni A, Pocovi M, El Messal M. Familial hypercholesterolemia associated with severe hypoalphalipoproteinemia in a Moroccan family. J Genet 2007; 86:159-63. [PMID: 17968143 DOI: 10.1007/s12041-007-0020-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Karima Ait Chihab
- Laboratoire de Biochimie et Biologiè Moleculaire, Groupe de Génétique et Biologie Molèculaire, Faculté des Sciences, Ain chock. B. P. 5366, Casablanca, Morocco
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Abstract
Atherosclerosis and its major clinical manifestation, coronary heart disease, is and will remain the main cause of mortality. Reviews on this subject dealt with factors that enhance development of atherosclerosis. This review deals with a new facet, that some individuals are less prone to develop atherosclerosis: (1) despite high cholesterol intake or (2) despite hypercholesterolemia with elevated low-density lipoprotein cholesterol (LDL-C) levels. The variability of response of plasma cholesterol to dietary intake was shown to be regulated by liver x receptor (LXR) that determines the rate of intestinal cholesterol absorption through the ATP-binding cassette (ABC) gene family. Other gene products, such as apolipoprotein-E (apo-E), scavenger receptor-B1 (SR-B1) and acyl coenzyme: cholesterol acyltransferase-2 (ACAT-2) affect cholesterol absorption also. The role of a genetic background for relative resistance to atherosclerosis is highlighted by subjects with familial hypercholesterolemia in whom high plasma cholesterol levels has not curtailed their expected life span. Studies in animals have shown that resistance to atherosclerosis in spite of hypercholesterolemia is affected by factors such as high-density lipoprotein (HDL) phospholipids that enhance reverse cholesterol transport, non-responsiveness to induction or lack of monocyte chemotactic protein-1 (MCP-1), C-C chemokine receptor 2 (CCR2), macrophage colony stimulating factor (MCSF), or vascular cell adhesion molecule-1 (VCAM-1). Since macrophages have been regarded as pro- or anti-atherogenic, evidence was collated that the high activity of scavenger receptors may contribute towards resistance to atherosclerosis if accompanied by adequate amounts of apo-E for cholesterol removal.
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MESH Headings
- Animals
- Apolipoproteins E/genetics
- Arteriosclerosis/complications
- Arteriosclerosis/genetics
- CD36 Antigens/genetics
- Carrier Proteins/genetics
- Chemokine CCL2/genetics
- Cholesterol/blood
- Cholesterol/genetics
- Cholesterol, Dietary
- Coronary Disease/complications
- Coronary Disease/genetics
- DNA-Binding Proteins
- Gene Expression Regulation/genetics
- Genetic Markers/genetics
- Genetic Predisposition to Disease/genetics
- Humans
- Hypercholesterolemia/complications
- Hypercholesterolemia/genetics
- Liver X Receptors
- Macrophage Colony-Stimulating Factor/genetics
- Membrane Proteins
- Orphan Nuclear Receptors
- Receptors, CCR2
- Receptors, Chemokine/genetics
- Receptors, Cytoplasmic and Nuclear
- Receptors, Immunologic
- Receptors, Lipoprotein
- Receptors, Retinoic Acid/genetics
- Receptors, Scavenger
- Receptors, Thyroid Hormone/genetics
- Scavenger Receptors, Class B
- Sterol O-Acyltransferase/genetics
- Vascular Cell Adhesion Molecule-1/genetics
- Vascular Resistance/genetics
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Affiliation(s)
- Olga Stein
- Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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7
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Carmena R, Roy M, Roederer G, Minnich A, Davignon J. Coexisting dysbetalipoproteinemia and familial hypercholesterolemia. Clinical and laboratory observations. Atherosclerosis 2000; 148:113-24. [PMID: 10580177 DOI: 10.1016/s0021-9150(99)00212-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Type III dysbetalipoproteinemia and familial hypercholesterolemia (FH) are two metabolic disorders giving rise to severe disturbances of lipid homeostasis and premature atherosclerosis. Both metabolic abnormalities have a genetic basis and co-occurrence in the same patient has seldom been described. Because of the unique structure of the French Canadian population, there was an opportunity to observe patients with both dysbetalipoproteinemia (E2/2 homozygotes) and FH (N=14) and to compare their clinical data with that of patients with type III (N=75), patients with FH (N0.7 and the presence of beta-VLDL on electrophoresis. Presence of a low density lipoprotein receptor, LDL-R, mutation should be suspected in a type III patient with a LDL-C level above 3.0 mmol/l and a family history of premature CAD. In the group of patients studied, the coexistence of dysbetalipoproteinemia and heterozygous FH does not appear to increase the prevalence of cardiovascular complications above that observed among control type III or control E3/3-FH patients. Thus, the presence of two epsilon2 alleles in these patients affects the expression of the abnormal LDL-R allele and the resulting phenotype substantiates the non additive effects of alleles at these two loci (epistasis).
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Affiliation(s)
- R Carmena
- Endocrine Service, Hospital Clinico Universitario, Valencia, Spain
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8
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Calandra S, Bertolinio S. Unusual inheritance of severe primary hypercholesterolemia. Atherosclerosis 1999; 144:464-6. [PMID: 10407508 DOI: 10.1016/s0021-9150(99)00095-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- S Calandra
- Dipartimento di Scienze Biomediche, Universita di Modena, Italy.
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9
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Abstract
The study of lipoprotein metabolism has led to major breakthroughs in the fields of cellular physiology, molecular genetics, and protein chemistry. These advances in basic science are reflected in medicine in the form of improved diagnostic methods and better therapeutic tools. Perhaps the greatest benefit is the improved ability to identify at an early stage patients who are at high risk for atherosclerosis, providing clinicians the opportunity to proceed swiftly with intensive lipid-lowering therapy for the prevention of cardiovascular complications. Recent clinical trials have shown that such an approach is not only cost-effective but saves lives while improving the quality of life. They also emphasize the important role physicians can have in prevention. More than half of patients with premature CAD have a familial form of dyslipoproteinemia. This review of the genetics of atherogenic lipoprotein disorders underscores the importance of identifying major genetic defects. It also stresses the need to take into account multifactorial etiologies and clustering of risk factors, as well as gene-gene and gene-environment interactions in assessing the atherogenic potential of a lipid transport disorder. Table 2 summarizes the key points in the diagnosis, clinical implications, and treatment of the major inherited atherogenic dyslipidemias.
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Affiliation(s)
- J Davignon
- Hyperlipidemia and Atherosclerosis Research Group, Clinical Research Institute of Montreal, Quebec, Canada
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10
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Pulai JI, Neuman RJ, Groenewegen AW, Wu J, Schonfeld G. Genetic heterogeneity in familial hypobetalipoproteinemia: Linkage and non-linkage to the apoB gene in caucasian families. ACTA ACUST UNITED AC 1998. [DOI: 10.1002/(sici)1096-8628(19980226)76:1<79::aid-ajmg15>3.0.co;2-m] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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11
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Koivisto UM, Gylling H, Miettinen TA, Kontula K. Familial moderate hypercholesterolemia caused by Asp235-->Glu mutation of the LDL receptor gene and co-occurrence of a de novo deletion of the LDL receptor gene in the same family. Arterioscler Thromb Vasc Biol 1997; 17:1392-9. [PMID: 9261272 DOI: 10.1161/01.atv.17.7.1392] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We identified a large family in which a hitherto unreported point mutation of the LDL receptor gene (Asp235-->Glu) cosegregated with moderately elevated serum LDL cholesterol concentration. Within one generation, the mean serum total and LDL cholesterol levels in four heterozygous carriers of this mutation (7.76 +/- 1.46 and 5.89 +/- 1.56 mmol/L, respectively) were significantly (P < .05) higher than the corresponding concentrations in their five nonaffected siblings (5.81 +/- 0.57 and 3.77 +/- 0.54 mmol/L, respectively). Lipid levels in carriers of the Asp235-->Glu mutation were, however, markedly lower than the corresponding total and LDL cholesterol levels (about 12 and 10 mmol/L, respectively) in heterozygous patients with the two common LDL receptor mutations (FH-Helsinki and FH-North Karelia). None of the four siblings in the age range of 54 to 69 years had experienced a myocardial infarction, although symptoms suggestive of coronary artery disease were present in two and tendon xanthomas were found in one. Expression of the mutant receptor in COS cells indicated an approximately 50% to 70% reduction of LDL-binding activity compared with the normal receptor. One patient (female, aged 39 years) had severe hypercholesterolemia in the range of 13 to 20 mmol/L when untreated, extensive coronary artery disease as demonstrated by angiography, and extensor tendon xanthomatosis. In addition to the Asp235-->Glu mutation, she was found to have a de novo deletion of exons 14 and 15 in her other LDL receptor allele. In this subject, the total LDL receptor activity of mitogen-stimulated blood lymphocytes was very low. In conclusion, along with another LDL receptor gene mutation (FH-Espoo or deletion of exon 15) described by us previously, the Asp235-->Glu mutation (designated as FH-Keuruu) indicates that moderate varieties of inherited hypercholesterolemia may result from LDL receptor gene mutations of mild expression.
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Affiliation(s)
- U M Koivisto
- Department of Medicine, University of Oulu, Finland
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12
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Nissen H, Hansen AB, Guldberg P, Petersen NE, Hansen TS, Hørder M. Detection and characterization of a novel splice mutation in the LDL receptor intron 12 resulting in two different mutant mRNA variants. Atherosclerosis 1997; 128:75-83. [PMID: 9051200 DOI: 10.1016/s0021-9150(96)05967-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Using a simple, standardized denaturing gradient gel electrophoresis (DGGE) based mutation screening technique, a novel G-to-A mutation in the last base of the intron 12 splice acceptor site of the LDL receptor gene was found in 2 Danish families with familial hypercholesterolemia (FH). The mutation is shown to result in 2 mRNA splice variants, both leading to truncated LDLR proteins, containing only the first 594 of the normal 839 amino acids. In one of the FH-families harbouring the mutation, a striking difference in the clinical picture amongst biochemically diagnosed FH patients was clarified when genetic analysis showed that 2 hypercholesterolemic family members, who despite advanced age had no atherosclerotic disease, had not inherited the family LDLR mutation. DGGE analyses of the LDLR exons, LDLR promoter, and apolipoprotein B codon 3456-3553 as well as Southern blotting of the LDLR gene were without signs of other mutations in the non-atherosclerotic hypercholesterolemics of the family. Availability of the clinically applicable mutation screening assay for FH may thus aid in defining reasons for phenotypic differences in FH families and potentially supply information allowing a more differentiated therapeutic approach to individual members of FH families.
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Affiliation(s)
- H Nissen
- Department of Clinical Chemistry, Odense University Hospital, Denmark
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Nissen H, Hansen AB, Guldberg P, Petersen NE, Larsen ML, Haghfelt T, Kristiansen K, Hørder M. Phenotypic presentation of the FH-Cincinnati type 5 low density lipoprotein receptor mutation. Scand J Clin Lab Invest 1996; 56:75-85. [PMID: 8850176 DOI: 10.1080/00365519609088591] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Familial hypercholesterolaemia (FH) is an autosomal dominant hereditary disease of lipid metabolism that in most families is caused by mutations in the low density lipoprotein receptor (LDLR) gene. Though more than 150 mutations are known, the clinical picture associated with most of these is not known. Genetic FH diagnosis may soon become routine in the setting of genetic counselling, and therefore thorough information on the phenotype-genotype relationship of different mutations is now important. In this study, index patients from each of 14 Danish FH families were screened for mutations in exon 2 of the LDLR gene using a denaturing gradient gel electrophoresis (DGGE)-based mutation screening assay. A deviating DGGE pattern identified two index patients, where subsequent sequencing revealed heterozygosity for the FH Cincinnati type 5 Trp23-to-Stop LDLR mutation. Data from three generations of the families allowed the first clinical and biochemical description of this mutation. Evidence that genetic analysis adds independent diagnostic information compared to traditional clinical/biochemical FH diagnosis was documented by demonstrating the presence of the FH Cincinnati mutation in a family member with a completely normal lipid profile. By comparison to non-FH family members, it was documented that carrier status for the FH Cincinnati mutation is associated with a significant risk of cardiovascular disease. Thus, genetic analysis may improve diagnostic precision and help to define more precisely which of the members of FH families are in need of preventive interventions and may aid in establishing phenotype-genotype relationships allowing more refined genetic counselling in FH.
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Affiliation(s)
- H Nissen
- Department of Clinical Chemistry, Odense University Hospital, Denmark
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14
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Sass C, Giroux LM, Lussier-Cacan S, Davignon J, Minnich A. Unexpected consequences of deletion of the first two repeats of the ligand-binding domain from the low density lipoprotein receptor. Evidence from a human mutation. J Biol Chem 1995; 270:25166-71. [PMID: 7559651 DOI: 10.1074/jbc.270.42.25166] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Heterozygosity for a 5-kilobase (kb) deletion of the first two ligand-binding repeats (exons 2 and 3) of the low density lipoprotein (LDL) receptor (R) gene (LDL-R delta 5kb) confers familial hypercholesterolemia (FH). The FH phenotype is unexpected based on previous site-directed mutagenesis showing that deletion of exons 2 and 3 resulted in little or no defect in LDL-R activity. In the present study, we took unique advantage of the ability to distinguish the LDL-R delta 5kb from the normal receptor on the basis of size, in order to resolve this apparent discrepancy. Fibroblasts from heterozygotes for the LDL-R delta 5kb displayed 50% of normal capacity to bind LDL and beta-VLDL, apparently due to lower receptor number. Cellular mRNA for the delta 5kb allele was at least as abundant as that for the normal allele. Immunoblotting and cell binding assays with anti-LDL-R antibody IgG-4A4 demonstrated normal synthesis and transport of the delta 5kb receptor. Ligand blotting demonstrated that the delta 5kb receptor displayed minimal or no ability to bind LDL or beta-VLDL. Thus, in contrast to transfected cell lines, in human fibroblasts, the first two cysteine rich repeats of the LDL-R appear functionally necessary. These characteristics of the LDL-R delta 5kb in human fibroblasts explain the in vivo phenotype of carriers.
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Affiliation(s)
- C Sass
- Department of Medicine, University of Montreal, Quebec, Canada
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