Biomedical subjects

A K Soutar

Publications and source records attributed to A K Soutar.

At least 19 recordsLinked to original sources

PubMed2006

Genetic causes of familial hypercholesterolaemia in patients in the UK: relation to plasma lipid levels and coronary heart disease risk.

AIMS: To determine the relative frequency of mutations in three different genes (low-density lipoprotein receptor (LDLR), APOB, PCSK9), and to examine their effect in development of coronary heart disease (CHD) in patients with clinically defined definite familial hypercholesterolaemia in UK. PATIENTS AND METHODS: 409 patients with familial hypercholesterolaemia patients (158 with CHD) were studied. The LDLR was partially screened by single-strand conformational polymorphism (SSCP) (exons 3, 4, 6-10 and 14) and by using a commercial kit for gross deletions or rearrangements. APOB (p.R3500Q) and PCSK9 (p.D374Y) were detected by specific assays. Coding exons of PCSK9 were screened by SSCP. RESULTS: Mutations were detected in 253 (61.9%) PATIENTS: 236 (57.7%) carried LDLR, 10 (2.4%) carried APOB p.Q3500 and 7 (1.7%) PCSK9 p.Y374. No additional mutations were identified in PCSK9. After adjusting for age, sex, smoking and systolic blood pressure, compared to those with no detectable mutation, the odds ratio of having CHD in those with an LDLR mutation was 1.84 (95% CI 1.10 to 3.06), for APOB 3.40 (0.71 to 16.36), and for PCSK9 19.96 (1.88 to 211.5; p = 0.001 overall). The high risk in patients carrying LDLR and PCSK9 p.Y374 was partly explained by their higher pretreatment cholesterol levels (LDLR, PCSK9 and no mutation, 10.29 (1.85), 13.12 and 9.85 (1.90) mmol/l, respectively, p = 0.001). The post-statin treatment lipid profile in PCSK9 p.Y374 carriers was worse than in patients with no identified mutation (LDL-C, 6.77 (1.82) mmol/l v 4.19 (1.26) mmol/l, p = 0.001, HDL-C 1.09 (0.27) mmol/l v 1.36 (0.36) mmol/l, p = 0.03). CONCLUSIONS: The higher CHD risk in patients carrying PCSK9 p.Y347 or a detected LDLR mutation supports the usefulness of DNA testing in the diagnosis and management of patients with familial hypercholesterolaemia. Mutations in PCSK9 appear uncommon in patients with familial hypercholesterolaemia in UK.

Adult↗

PubMed2001

Fh-Souassi: a founder frameshift mutation in exon 10 of the LDL-receptor gene, associated with a mild phenotype in Tunisian families.

Familial hypercholesterolemia (FH) has a higher prevalence in central Tunisia together with a milder clinical expression than in western countries. The molecular basis of FH in Tunisia remains unknown. Our aim was to identify FH-causing mutations in three unrelated families (21 subjects) from the area of Souassi (central Tunisia). In probands with a presentation of homozygous FH, the promoter and 18 exons of the low density lipoprotein (LDL)-receptor gene were sequenced in both orientations. A novel complex frameshift mutation was identified in exon 10, nucleotides 1477-1479 (TCT) at Serine 472 were replaced by an insertion of seven nucleotides (AGAGACA), producing a premature termination codon 43 amino acids downstream. Binding of 125I-labelled LDL at 4 degrees C to cultured fibroblasts from two probands showed <2% normal LDL-receptor activity. AvaII digestion of PCR amplified genomic DNA identified this unique mutation in all families; homozygotes n=11, heterozygotes n=10. All mutation carriers shared the same haplotype (7 RFLPs), suggesting that they had a common ancestor. Despite high plasma LDL levels (m=16.0+/-3.0 mmol/l) and extravascular cholesterol deposits, most homozygotes were diagnosed after puberty and had a delayed onset of cardiovascular complications. Moreover, most heterozygotes were free of clinical signs and had plasma LDL cholesterol in the normal range (4.7+/-1.3 mmol/l) without taking any lipid-lowering medication. This mild clinical phenotype which contrasted with the severity of the mutation, could not be explained by specific apolipoprotein E or lipoprotein lipase alleles.

Adolescent↗

PubMed2001

Use of homozygosity mapping to identify a region on chromosome 1 bearing a defective gene that causes autosomal recessive homozygous hypercholesterolemia in two unrelated families.

Familial hypercholesterolemia (FH) is a common inherited disorder of metabolism characterized clinically by high levels of low-density lipoprotein (LDL) in plasma owing to reduced catabolism. This leads to accelerated atherosclerosis and thus to an increased risk of coronary heart disease. FH is usually caused by defects in the gene for either the LDL receptor or apolipoprotein B (apoB), the ligand for the LDL receptor. Elsewhere, we have described two unrelated patients with phenotypic homozygous FH. Both patients were offspring of consanguineous unions, and linkage to either the gene for the LDL receptor or the gene for apoB was excluded in both. Their cells in culture do not degrade LDL, despite the presence of normal surface binding of LDL to the LDL receptor. This observation suggests that the patients may be homozygous for a defective gene that encodes a component of the internalization pathway. We first excluded linkage of the defect to known genes for proteins reported to be involved in internalization of receptors in clathrin-coated pits. We then performed genomewide homozygosity mapping. Genotyping of 500 polymorphic markers in three affected and seven unaffected members of the first pedigree showed that recessive hypercholesterolemia in this family is localized to a single chromosomal region on 1p36-p35. Genotyping of two affected and five unaffected members of the second pedigree provided further evidence of linkage to this locus, thereby mapping the disease-causing gene to a 12-cM region on chromosome 1p36-p35, with a combined LOD score of 5.3 in these unrelated families. Identification of the gene in this region may lead to new insights into the mechanisms of LDL receptor-mediated uptake of LDL by cells and may help to identify further genetic risk factors for premature atherosclerosis.

Cells, Cultured↗

PubMed2001

Determinants of variable response to statin treatment in patients with refractory familial hypercholesterolemia.

Interindividual variability in low density lipoprotein (LDL) cholesterol (LDL-C) response during treatment with statins is well documented but poorly understood. To investigate potential metabolic and genetic determinants of statin responsiveness, 19 patients with refractory heterozygous familial hypercholesterolemia were sequentially treated with placebo, atorvastatin (10 mg/d), bile acid sequestrant, and the 2 combined, each for 4 weeks. Levels of LDL-C, mevalonic acid (MVA), 7-alpha-OH-4-cholesten-3-one, and leukocyte LDL receptor and hydroxymethylglutaryl coenzyme A reductase mRNA were determined after each treatment period. Atorvastatin (10 mg/d) reduced LDL-C by an overall mean of 32.5%. Above-average responders (LDL-C -39.5%) had higher basal MVA levels (34.4+/-6.1 micromol/L) than did below-average responders (LDL-C -23.6%, P<0.02; basal MVA 26.3+/-6.1 micromol/L, P<0.01). Fewer good responders compared with the poor responders had an apolipoprotein E4 allele (3 of 11 versus 6 of 8, respectively; P<0.05). There were no baseline differences between them in 7-alpha-OH-4-cholesten-3-one, hydroxymethylglutaryl coenzyme A reductase mRNA, or LDL receptor mRNA, but the latter increased in the good responders on combination therapy (P<0.05). Severe mutations were not more common in poor than in good responders. We conclude that poor responders to statins have a low basal rate of cholesterol synthesis that may be secondary to a genetically determined increase in cholesterol absorption, possibly mediated by apolipoprotein E4. If so, statin responsiveness could be enhanced by reducing dietary cholesterol intake or inhibiting absorption.

Anticholesteremic Agents↗

PubMed2001

Localization of apolipoprotein E receptor 2 to caveolae in the plasma membrane.

The LDL receptor (LDL-R) promotes the specific endocytosis and lysosomal delivery of extracellular lipoprotein ligands via clathrin-coated pits. It was widely assumed that other closely related members of the LDL-R gene family would have similar functions, but recent experimental evidence has revealed that one such protein, apolipoprotein E receptor 2 (apoER2), has a critical role as an "outside-in" signal transducer in the brain. ApoER2 signaling appears to require interaction between its cytoplasmic domain and adapter molecules such as Dab1, JIP 1 and JIP 2, and PSD-95. Many of the receptors for other signaling pathways affected by such adapter molecules are compartmentalized into specialized microdomains within the plasma membrane termed caveolae. Here, we show that apoER2, but not LDL-R, is localized to caveolae, supporting the concept that its physiological role is in cell signaling, rather than in endocytosing ligands.

Alternative Splicing↗

PubMed2000

The effect of peroxisome-proliferator-activated receptor-alpha on the activity of the cholesterol 7 alpha-hydroxylase gene.

Cholesterol 7 alpha-hydroxylase (Cyp7a1) plays a central role in the regulation of bile acid and cholesterol metabolism, and transcription of the gene is controlled by bile acids and hormones acting through a complex interaction with a number of potential steroid-hormone-binding sites. Transcriptional activity of the human CYP7A1 gene promoter transfected into HepG2 cells was decreased in a concentration-dependent manner by co-transfection with an expression vector for peroxisome-proliferator-activated receptor-alpha (PPAR alpha). This effect was augmented by 9-cis-retinoic acid receptor-alpha (RXR alpha) and activators of PPAR alpha to give a maximum inhibition of approx. 80%. The region responsible for this inhibition contained a site known to bind hepatocyte nuclear factor 4 (HNF4), and mutation of this site greatly decreased the effect. Co-expression of HNF4 increased promoter activity and decreased the effect of PPAR alpha. Gel-mobility-shift assays failed to detect any binding of PPAR alpha/RXR alpha dimers to any regions of the promoter containing potential binding sites. Also the hepatic abundance of Cyp7a1 mRNA in mice in which the PPAR alpha gene was disrupted was the same as in normal mice, both during the dark phase, when the animals were feeding, and during the light phase, when mRNA abundance was greatly increased. Cholesterol feeding produced the same increase in hepatic Cyp7a1 mRNA abundance in PPAR alpha-null animals as in normals. It is concluded that, whereas PPAR alpha can affect CYP7A1 gene transcription in vitro through an indirect action, probably by competing for co-factors, this is unlikely to be a major influence on Cyp7a1 activity under normal physiological conditions.

Animals↗

PubMed2000

Expression of an LDL receptor allele with two different mutations (E256K and I402T).

AIMS: To investigate the disease causing event in patients with familial hypercholesterolaemia, carrying two mutations each, E256K in exon 6 and I402T in exon 9, of the gene encoding the low density lipoprotein (LDL) receptor. It was not known whether the mutations were positioned in cis or trans, or if they were each pathogenic separately or only when present together. METHODS: Polymerase chain reaction, denaturing gradient gel electrophoresis and sequencing were used to characterise the LDL receptor locus of the patients and family members. The different LDL receptor mutants, constructed in vitro by oligonucleotide directed mutagenesis, were expressed in LDL receptor deficient Chinese hamster ovary (CHO1d1A7) cells, to determine the effects of the mutations on LDL receptor function. RESULTS: The two mutations were located on the same allele of the LDL receptor gene. All mutant constructs resulted in the production of a detectable protein in CHO cells. The cells expressing only the I402T mutation, or the combination of I402T and E256K mutations, were seriously affected in mediating uptake and degradation of LDL. Contrary to initial predictions, the cells expressing only the E256K mutation showed essentially the same binding, uptake, and degradation of 125I labelled LDL as cells transfected with normal LDL receptor cDNA. These results suggest that the pathogenic mutation in the patients heterozygous for the E256K/I402T allele is the I402T mutation, and that E256K alone is a rare sequence variation, which does not affect LDL receptor protein function. E256K was not detected either in DNA from a healthy population or in DNA from other hypercholesterolaemic patients studied. CONCLUSIONS: Despite the information available on the structure-function relations between the LDL receptor and LDL receptor like proteins, predictions about the disease causing potential of a mutation are not reliable. These results suggest that the I402T mutation is pathogenic and that the substitution of E256K alone is a rare sequence variation, without a detectable phenotype modulating effect.

Alleles↗

PubMed1999

An individual with a healthy phenotype in spite of a pathogenic LDL receptor mutation (C240F).

Familial hypercholesterolemia (FH) is caused by a defect in the function of the low density lipoprotein (LDL) receptor and inherited in an autosomal, codominant way. In this study we present a 13-year-old girl, compound heterozygote for the LDL receptor mutations C240F and Y167X. Fibroblasts from the patient showed very low cholesterol esterification rate, LDL uptake, and degradation compared to normal fibroblasts (< 2%, 8%, and < 2%, respectively). The C240F mutant was expressed in LDL receptor deficient CHOMldlA7 cells. Analysis of cell extracts by immunoblotting demonstrated delayed processing of the mutated LDL receptor, which was accumulated as a precursor protein of normal size. A high molecular weight form of the receptor was also detectable in these cells, which probably reflects cross-linking through the unpaired cysteine residue in the binding domain. Cells expressing the C240F mutant protein were unable to mediate uptake and degradation of LDL. The two siblings of the index case also carried the C240F mutation, but surprisingly one of them (a 17-year-old brother) showed no signs of hypercholesterolemia. This observation is consistent with the view that there may be cholesterol lowering mechanisms that can be activated, perhaps by mutations in known or hitherto unknown genes.

Adolescent↗

PubMed1999

Inheritance of two different alleles of the low-density lipoprotein (LDL)-receptor gene carrying the recurrent Pro664Leu mutation in a patient with homozygous familial hypercholesterolaemia.

Familial hypercholesterolaemia (FH) is caused by mutations in the low-density lipoprotein (LDL)-receptor gene that result in impaired clearance of plasma LDL and increased risk of coronary heart disease. Numerous different mutations have been found in FH patients worldwide, the majority of which are infrequent in out-bred populations and account for 2% or less of patients with the disorder in large cohorts. Thus, it was surprising to find that two homozygous FH patients referred to a single hospital in the UK were both apparently homozygous for the Pro664Leu mutation. One, an Asian patient, was a true homozygote. The other, of English origin, had inherited two different alleles of the LDL-receptor gene with the same mutation from unrelated parents, as inferred from the haplotype of polymorphic markers. A third, clinically homozygous FH patient, despite being the offspring of first cousins, had inherited one 'Asian' Pro664Leu allele, but an allele with a 1-bp deletion in exon 5 from the other parent. The Pro664Leu mutation in the LDL-receptor gene has now been described in heterozygous patients of very different ethnic origin and is associated with different haplotypes, suggesting that the same base change at a CpG may have recurred as many as six times.

Alleles↗

PubMed1999

Expression in vitro of alternatively spliced variants of the messenger RNA for human apolipoprotein E receptor-2 identified in human tissues by ribonuclease protection assays.

The apolipoprotein E receptor-2 (apoER2), also called LR7/8B, is a member of the low-density lipoprotein (LDL)-receptor family that is expressed in brain. We have identified mRNA splicing variants in human tissues by ribonuclease protection assays and found that some variants are preferentially amplified by reverse transcription-polymerase chain reaction (RT-PCR). Transcripts were found that lacked sequences encoding three repeats in the putative ligand-binding domain, the O-linked sugar domain or a novel region in the cytoplasmic domain. When mammalian expression vectors for eight potential protein isoforms were transfected into LDL-receptor-deficient Chinese hamster ovary cells, the proteins were all expressed on the cell surface, as detected by immunoblotting of cell extracts with a specific antipeptide antiserum to apoER2 before and after treatment of intact cells with pronase. Although cells expressing all the variants bound very low-density lipoprotein of beta mobility (beta-VLDL), it was with lower affinity and capacity than binding by the LDL-receptor and none was able to degrade beta-VLDL. Ligand blotting of cell extracts showed that all variants bound recombinant histidine6-tagged receptor-associated protein (His6-RAP) with high affinity, although variants lacking exon 5 bound less strongly. The presence of vestiges of the novel insert in the cytoplasmic domain of apoER2 in the LDL- or VLDL-receptor genes was investigated, but nucleotide sequencing showed that no sequences homologous to it could be detected in the final intron of these genes.

Alternative Splicing↗

PubMed1999

Characterization of a novel cellular defect in patients with phenotypic homozygous familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is characterized by a raised concentration of LDL in plasma that results in a significantly increased risk of premature atherosclerosis. In FH, impaired removal of LDL from the circulation results from inherited mutations in the LDL receptor gene or, more rarely, in the gene for apo B, the ligand for the LDL receptor. We have identified two unrelated clinically homozygous FH patients whose cells exhibit no measurable degradation of LDL in culture. Extensive analysis of DNA and mRNA revealed no defect in the LDL receptor, and alleles of the LDL receptor or apo B genes do not cosegregate with hypercholesterolemia in these families. FACS((R)) analysis of binding and uptake of fluorescent LDL or anti-LDL receptor antibodies showed that LDL receptors are on the cell surface and bind LDL normally, but fail to be internalized, suggesting that some component of endocytosis through clathrin-coated pits is defective. Internalization of the transferrin receptor occurs normally, suggesting that the defective gene product may interact specifically with the LDL receptor internalization signal. Identification of the defective gene will aid genetic diagnosis of other hypercholesterolemic patients and elucidate the mechanism by which LDL receptors are internalized.

Adolescent↗

PubMed1999

Transcription factors CCAAT/enhancer-binding protein beta and nuclear factor-Y bind to discrete regulatory elements in the very low density lipoprotein receptor promoter.

Expression of the very low density lipoprotein receptor (VLDL-R) is barely detectable in liver, but occurs in adipose tissue, skeletal muscle, heart, and placenta, where it is postulated to supply triglyceride to tissues that utilize fatty acids. To investigate its tissue-specific expression, cell lines were transfected with luciferase reporter gene constructs driven by the 5'-flanking region of the VLDL-R gene. Transcriptional activity of a 4.2-kb promoter fragment was 5-fold higher in BeWo placental cells than in Huh-7 hepatoma cells, consistent with relative endogenous expression of the VLDL-R. By deletion analysis, DNase I protection assays and site-directed mutagenesis, two regulatory elements were essential for maximal promoter activity in BeWo cells: footprint site D (-856 to -830) and an inverted CCAAT box (-703 to -707). Mutation of either element reduced promoter activity by 60% in BeWo cells, but had little effect in Huh-7 cells, suggesting that these elements direct cell-type specific transcription. Electrophoretic mobility-shift assays with BeWo nuclear extracts revealed that the inverted CCAAT box binds transcription factor NF-Y, and site D binds CCAAT/enhancer-binding protein b (C/EBPbeta) and minor amounts of C/EBPalpha and C/EBPdelta. Overexpression of a dominant negative NF-YA vector confirmed involvement of NF-Y in the regulation of the VLDL-receptor gene through the CCAAT box. However overexpression of C/EBP could not stimulate transcription from the VLDL-receptor promoter nor from site D fused to a heterologous promoter, suggesting that the simultaneous binding of an accessory factor(s) may be necessary for C/EBP transactivation via the D site.

CCAAT-Enhancer-Binding Proteins↗

PubMed1998

Influence of genotype at the low density lipoprotein (LDL) receptor gene locus on the clinical phenotype and response to lipid-lowering drug therapy in heterozygous familial hypercholesterolaemia. The Familial Hypercholesterolaemia Regression Study Group.

The relationship between molecular defect and clinical phenotype has been examined in 42 patients with heterozygous familial hypercholesterolaemia (FH) and premature coronary heart disease. The defined defects included mutations in the low density lipoprotein (LDL)-receptor gene (23/42) or the apolipoprotein B Arg3500Gln mutation (5/42). Mean LDL-cholesterol was higher, both before and during treatment with simvastatin and bile acid sequestrants, in patients predicted as having a 'severe' mutation than in those with a 'mild' mutation (8.72 +/- 2.02 mmol/l vs 6.63 +/- 1.8, P = 0.05 before and 4.51 +/- 0.90 mmol/l vs 3.19 +/- 0.58, P = 0.05 during treatment). Maximum inducible LDL-receptor activity in cultured lymphoblasts was inversely correlated with LDL-cholesterol before (r2 = 0.499, P = 0.002) and during (r2 = 0.478, P = 0.004) treatment in patients with a defined mutation in the LDL-receptor gene, but not in the 14 patients with no detectable molecular defect. LDL-cholesterol concentrations before and during treatment were significantly correlated in patients with a defined LDL-receptor gene mutation (r2 = 0.548, P = 0.0001), but not in those with no detectable genetic defect. All these correlations were weak, however and there were no differences in the response to treatment in terms of either relative reduction or absolute decrease in LDL-cholesterol concentration between patients with different LDL-receptor defects. We conclude that only part of the variable phenotype of heterozygous FH patients is explained by different LDL-receptor defects and that other factors determine the severity of their hypercholesterolaemia and the onset of coronary disease.

Adult↗

PubMed1998

Update on low density lipoprotein receptor mutations.

Recent research has focused on the rapid detection of new LDL receptor gene variants and large scale screening for known mutations. Whether the nature of the mutation in the LDL receptor gene in familial hypercholesterolaemia determines clinical variability has been examined, as well as the potential value of detecting mutation carriers for clinical practice. There is also evidence that some patients with clinical familial hypercholesterolaemia do not have detectable defects in the LDL receptor or apolipoprotein B.

Databases, Factual↗

PubMed1998

Phenotypic variation in heterozygous familial hypercholesterolemia: a comparison of Chinese patients with the same or similar mutations in the LDL receptor gene in China or Canada.

Familial hypercholesterolemia (FH) is caused by mutations in the LDL receptor (LDLR) gene and is usually associated with hypercholesterolemia, lipid deposition in tissues, and premature coronary artery disease (CAD). However, individuals with heterozygous FH in China exhibit a milder phenotype despite having deleterious mutations in the LDLR gene (X.-M. Sun et al, Arterioscler Thromb. 1994;14:85-94). Nineteen Chinese FH heterozygotes living in Canada were screened for the 11 mutations that had been described in FH patients living in China. One Chinese Canadian carried one of these mutations (Trp462Stop), 2 carried a previously unreported single-base substitution (Cysl63Arg), and 1 carried a mutation observed in French-Canadian patients (Glu207Lys). Twelve additional carriers of these mutations were identified in the families of the index patients. Significantly higher LDL cholesterol concentrations were observed in FH heterozygotes with defined mutations living in Canada (mean+/-SD, 7.46+/-1.29, n=16) than in those living in China (4.35+/-1.09, n=18; P<.0001). Six of the 16 FH heterozygotes residingin Canada had evidence of tendon xanthomata and 4 had a history of premature CAD, whereas none of those in China had tendon xanthomata or CAD. Complete segregation between hypercholesterolemia and inheritance of a mutant allele was observed in 3 Canadian Chinese FH families. Thus, Chinese FH heterozygotes living in Canada exhibit a phenotype similar to that of other FH patients in Western societies. The difference between patients living in Canada and those living in China could be ascribed to differences in dietary fat consumption, showing that environmental factors such as diet play a significant role in modulating the phenotype of heterozygous FH.

Adult↗

PubMed1997

Synthesis and properties of the very-low-density-lipoprotein receptor and a comparison with the low-density-lipoprotein receptor.

The properties of the very-low-density lipoprotein (VLDL) receptor have been studied in Chinese hamster ovary (CHO) cells stably transfected with human VLDL-receptor cDNA and compared with those of the low-density lipoprotein (LDL) receptor expressed under the same conditions. Immunoblotting showed that the cells produced a mature VLDL receptor protein, of apparent Mr 123000 on non-reduced and 158000 on reduced gels, that was less extensively glycosylated than the LDL receptor. The VLDL receptor was more slowly processed than the LDL receptor, with only approx. 70% of the precursor being converted into the mature protein. Nevertheless, the majority of the receptor in the cells was in the mature form, and most of this was present on the cell surface. The human VLDL receptor bound rabbit very-low-density lipoprotein with beta electrophoretic mobility (betaVLDL), but not human LDL, and uptake through the receptor led to stimulation of oleate incorporation into cholesteryl esters. At 37 degrees C, the characteristics of VLDL-receptor-mediated uptake and degradation of betaVLDL were essentially the same as those mediated by the LDL receptor. However, the VLDL receptor apparently did not show the increase in affinity and decrease in binding of betaVLDL on cooling to 4 degrees C that was exhibited by the LDL receptor. Thus the overexpressed VLDL receptor in CHO cells appears to behave as a lipoprotein receptor with similar, but not identical, properties to the LDL receptor.

Animals↗

PubMed1997

Comparison of the genetic defect with LDL-receptor activity in cultured cells from patients with a clinical diagnosis of heterozygous familial hypercholesterolemia. The Familial Hypercholesterolaemia Regression Study Group.

In this study we have analyzed the genetic defect in 42 patients with a diagnosis of heterozygous familial hypercholesterolemia (FH) by Southern blotting, SSCP, and sequencing of PCR-amplified fragments of genomic DNA or sequencing of RT-PCR products from mRNA in cultured cells. The apoB Arg3500Gln mutation was identified in five patients. A molecular defect in the LDL-receptor gene was confirmed in 23 patients; 16 of these mutations have not been described before. No defect in the coding region, intron:exon junctions or proximal promoter of the LDL-receptor gene or in the region of the apoB gene coding for the LDL-receptor binding domain was found in the remaining 14 patients. LDL-receptor activity and protein content of cultured lymphoblasts from the patients was significantly lower in cells from patients with severe rather than mild LDL-receptor mutations. Cells from four patients with no detectable defect showed reduced LDL receptor activity compared with eight normal cell lines, whereas six others had reduced LDL-receptor activity but LDL-receptor protein content within the normal range. Cells from four patients appeared to have normal LDL-receptor function. Cells from two patients with a defined defect also had LDL-receptor activity within the normal range. The findings demonstrate the problems involved in the genetic diagnosis of FH in patients.

Adult↗

PubMed1996

Hereditary hepatic and systemic amyloidosis caused by a new deletion/insertion mutation in the apolipoprotein AI gene.

We report a Spanish family with autosomal-dominant non-neuropathic hereditary amyloidosis with a unique hepatic presentation and death from liver failure, usually by the sixth decade. The disease is caused by a previously unreported deletion/insertion mutation in exon 4 of the apolipoprotein AI (apoAI) gene encoding loss of residues 60-71 of normal mature apoAI and insertion at that position of two new residues, ValThr. Affected individuals are heterozygous for this mutation and have both normal apoAI and variant molecules bearing one extra positive charge, as predicted from the DNA sequence. The amyloid fibrils are composed exclusively of NH2-terminal fragments of the variant, ending mainly at positions corresponding to residues 83 and 92 in the mature wild-type sequence. Amyloid fibrils derived from the other three known amyloidogenic apoAI variants are also composed of similar NH2-terminal fragments. All known amyloidogenic apoAI variants carry one extra positive charge in this region, suggesting that it may be responsible for their enhanced amyloidogenicity. In addition to causing a new phenotype, this is the first deletion mutation to be described in association with hereditary amyloidosis and it significantly extends the value of the apoAI model for investigation of molecular mechanisms of amyloid fibrillogenesis.

Adult↗