Evidence for a cholesterol-lowering gene in a French-Canadian kindred with familial hypercholesterolemia

Sass, Catherine; Giroux, L; Ma, Yuanhong; Roy, Madeleine; Lavigne, Jacques; Lussier‐Cacan, Suzanne; Davignon, Jean; Minnich, Anne

doi:10.1007/bf00214181

Cited by 15 publications

(8 citation statements)

References 34 publications

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“…LDL-R mRNA in LDL-R ⌬5kb Fibroblasts-Although LDL-R activity in LDL-R ⌬5kb fibroblasts was only 50 -60% that of normal cells, the ratio of LDL-R mRNA to that for ␤-actin in fibroblasts and in lymphocytes was similar in carriers and non-carriers (7). To compare the relative amount of LDL-R mRNA corresponding to the deleted allele with that of the normal allele, primers surrounding the deletion were designed (see "Materials and Methods").…”

Section: Resultsmentioning

confidence: 93%

“…Oligonucleotides were synthesized by the solid phase triester method on a Pharmacia LKB Gene Assembler Plus DNA synthesizer. The ratio of fibroblast and lymphocyte LDL-R mRNA to that for ␤-actin was quantified by RT-PCR and fluorescence DNA detection as described (7). In LDL-R ⌬5kb HTZ cells, the relative expression of the deleted versus the normal LDL-R allele was determined by amplification of the cDNA with fluorescent primers 5Ј-cgccgcggcggggactgcag-3Ј and 5Ј-agttttcctcgtcagtttgtc-3Ј, yielding polymerase chain reaction fragments of 638 and 441 nucleotides for the normal and deleted allele, respectively.…”

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confidence: 99%

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Unexpected Consequences of Deletion of the First Two Repeats of the Ligand-binding Domain from the Low Density Lipoprotein Receptor

Sass

Giroux

Lussier‐Cacan

et al. 1995

Journal of Biological Chemistry

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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 ⌬5kb) confers familial hypercholesterolemia (FH).The FH phenotype is unexpected based on previous sitedirected 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 ⌬5kb from the normal receptor on the basis of size, in order to resolve this apparent discrepancy. Fibroblasts from heterozygotes for the LDL-R ⌬5kb displayed 50% of normal capacity to bind LDL and ␤-VLDL, apparently due to lower receptor number. Cellular mRNA for the ⌬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 ⌬5kb receptor. Ligand blotting demonstrated that the ⌬5kb receptor displayed minimal or no ability to bind LDL or ␤-VLDL. Thus, in contrast to transfected cell lines, in human fibroblasts, the first two cysteinerich repeats of the LDL-R appear functionally necessary. These characteristics of the LDL-R ⌬5kb in human fibroblasts explain the in vivo phenotype of carriers. The low density lipoprotein (LDL)1 receptor (R) binds and catabolizes apolipoprotein E-containing chylomicron and VLDL remnants and LDL. In the liver, LDL-R functions to remove these lipoproteins from plasma for eventual excretion of the cholesterol into the bile. In peripheral cells, it functions to provide the cell with cholesterol needed for membrane synthesis. The LDL-R contains five major structural domains: a seven-repeat, cysteine-rich ligand binding domain encoded by exons 2-6, an epidermal growth factor-precursor homology domain (exons 7-14), a glycosylation domain (exon 15), a membrane-spanning domain (exon 16), and a cytoplasmic tail (exon 17) (1). The LDL-R is one of the few proteins for which knowledge of the structure-function relationship has been generated both from site-directed mutagenesis and from numerous naturally occurring human mutations.Mutations in the LDL-R gene resulting in a dysfunctional receptor cause a codominantly inherited disorder of plasma cholesterol catabolism known as familial hypercholesterolemia (FH). Human LDL-R mutations have been assigned to five classes of defects based on their phenotypic effects on the receptor protein (1). We have previously described a deletion of approximately 5 kb, which removes exons 2 and 3 of the LDL-R gene (LDL-R ⌬5kb) (2). In site-directed mutagenesis experiments, deletion of the first repeat (exon 2) has no effect on the binding or internalization of LDL or ␤-VLDL or recycling of receptors in transfected mammalian cells (3). Simultaneous deletion of exons 2 and 3 has resulted in a receptor which binds LDL 70% as well as the normal receptor and which binds ␤-VLDL equally as well (4). These results have led to the suggestion that the first two repeats of the LDL-R ligandb...

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Section: Resultsmentioning

confidence: 93%

mentioning

confidence: 99%

Unexpected Consequences of Deletion of the First Two Repeats of the Ligand-binding Domain from the Low Density Lipoprotein Receptor

Sass

Giroux

Lussier‐Cacan

et al. 1995

Journal of Biological Chemistry

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“…Neither the genetic nor the physiologic basis for the low apoAI are known. Many of the subjects in the kindreds reported by Fazio et al [1991], Hobbs et al [1989], and Sass et al [1995] also presented with low levels of HDL and apoAI. It is not clear, whether this is a coincidence or a characteristic of non-apoB-linked FHBL kindreds.…”

Section: Discussionmentioning

confidence: 91%

“…In 1 kindred with FHBL, linkage to apoB has been ruled out, but the gene responsible was not identified [Fazio et al, 1991]. In 2 kindreds with familial hypercholesterolemia (FH) the segregation of a ''cholesterol suppressor gene'' that produces lower than expected cholesterol levels has been noted [Sass et al, 1995;Hobbs et al, 1989]. The responsible genes are unknown, but the apoB gene has been ruled out.…”

Section: Discussionmentioning

confidence: 96%

Genetic heterogeneity in familial hypobetalipoproteinemia: Linkage and non-linkage to the apoB gene in caucasian families

et al. 1998

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Familial hypobetalipoproteinemia (FHBL) is an autosomal dominant disorder of lipid metabolism characterized by extremely low plasma levels of apolipoprotein B (apoB), and total-, and low-density lipoprotein (LDL) cholesterol. Various truncated forms of apoB have been found to cosegregate with the FHBL phenotype in more than 30 kindreds. By contrast, no truncated forms of apoB protein were detected with sensitive immunoblotting in the plasmas of any of the 6 kindreds reported here. Individuals with apoB levels in the 5th centile for their age and sex were considered as affected with FHBL. Linkage analysis was performed using 3 microsatellite markers flanking the apoB gene (D2S131, D2S149, and D2S144), a 3' variable number of tandem repeats (VNTR) marker and one intragenic marker. Two-point linkage of FHBL was established to the 3' VNTR marker with a combined maximum LOD score of 8.5 at theta = 0 for 5 of the 6 families. Maximum LOD scores for flanking microsatellite markers were 5.0, 2.4, 1.3, 1.2 and 2.1 for these kindreds (D, T, De, C and Z, respectively). A test of homogeneity differentiated the 6th family (F kindred) from the other five. LOD scores of -25.2 at the 3' VNTR and -7.8 at the intragenic apoB/Xbal marker at theta = 0 excluded linkage to the apoB gene in the F kindred. These kindreds demonstrate the heterogeneity of FHBL and also offer the possibility to investigate as yet undescribed mutations of apoB, resulting in alterations of apoB metabolism. The F kindred may shed light on novel gene(s) contributing to the low apoB-phenotype.

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“…Indeed, there is an extreme variability of the hypercholesterolemic phenotype with well-documented cases of incomplete penetrance probably due to the effect of modifier factors. For example, Sass et al 19 reported a French Canadian family with a 5 kb deletion in the LDLR gene with several carriers of the mutation presenting normal cholesterol values. In the same manner, Hobbs et al 20 described a large Puerto Rican family carrying the p.Ser156Leu (now p.Ser177Leu according to the international nomenclature) mutation of the LDLR gene.…”

Section: Discussionmentioning

confidence: 99%

A fourth locus for autosomal dominant hypercholesterolemia maps at 16q22.1

Marques-Pinheiro¹,

Marduel²,

Rabès³

et al. 2010

Eur J Hum Genet

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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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Evidence for a cholesterol-lowering gene in a French-Canadian kindred with familial hypercholesterolemia

Cited by 15 publications

References 34 publications

Unexpected Consequences of Deletion of the First Two Repeats of the Ligand-binding Domain from the Low Density Lipoprotein Receptor

Unexpected Consequences of Deletion of the First Two Repeats of the Ligand-binding Domain from the Low Density Lipoprotein Receptor

Genetic heterogeneity in familial hypobetalipoproteinemia: Linkage and non-linkage to the apoB gene in caucasian families

A fourth locus for autosomal dominant hypercholesterolemia maps at 16q22.1

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