Browsing by Author "Soutar, A.K."
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- Familial hypercholesterolaemia in PortugalPublication . Bourbon, M.; Alves, A.C.; Medeiros, A.M.; Silva, S.; Soutar, A.K.; Investigators of Portuguese FH StudyFamilial hypercholesterolaemia (FH) is characterised clinically by an increased level of circulating LDL cholesterol that leads to lipid accumulation in tendons and arteries, premature atherosclerosis and increased risk of coronary heart disease (CHD). Although Portugal should have about 20,000 cases, this disease is severely under-diagnosed in our country, this being the first presentation of Portuguese data on FH. A total of 602 blood samples were collected from 184 index patients and 418 relatives from several centres throughout Portugal. Fifty-three different mutations were found in 83 index patients, 79 heterozygous and 4 with two defective LDLR alleles. Additionally, 4 putative alterations were found in 8 patients but were not considered mutations causing disease, mainly because they did not co-segregate with hypercholesterolaemia in the families. Three unrelated patients were found to be heterozygous for the APOB(3500) mutation and two unrelated patients were found to be heterozygous for a novel mutation in PCSK9, predicted to cause a single amino acid substitution, D374H. Cascade screening increased the number of FH patients identified genetically to 204. The newly identified FH patients are now receiving counselling and treatment based on the genetic diagnosis. The early identification of FH patients can increase their life expectancy and quality of life by preventing the development of premature CHD if patients receive appropriate pharmacological treatment.
- Genetic diagnosis of familial hypercholesterolaemia: the importance of functional analysis of potential splice-site mutationsPublication . Bourbon, M.; Duarte, M.A.; Alves, A.C.; Medeiros, A.M.; Marques, L.; Soutar, A.K.Familial hypercholesterolemia (FH) results from defective low-density lipoprotein receptor (LDLR) activity, mainly due to LDLR gene defects. Of the many different LDLR mutations found in patients with FH, about 6% of single base substitutions are located near or within introns, and are predicted to result in exon skipping, retention of an intron, or activation of cryptic sites during mRNA splicing. This paper reports on the Portuguese FH Study, which found 10 such mutations, 6 of them novel. For the mutations that have not been described before or those whose effect on function have not been analysed, their effect on splicing was investigated, using reverse transcriptase PCR analysis of LDLR mRNA from freshly isolated blood mononuclear cells. Two of these variants (c.313+6 T-->C, c.2389G-->T (p.V776L)) caused exon skipping, and one caused retention of an intron (c.1359-5C-->G), whereas two others (c.2140+5 G-->A and c.1061-8T-->C) had no apparent effect. Any effect of c.1185G-->C (p.V374V) on splicing could not be determined because it was on an allele with a promoter mutation (-42C-->G) that was probably not transcribed. Variants in four patients lost to follow-up could not be tested experimentally, but they almost certainly affect splicing because they disrupt the invariant AG or GT in acceptor (c.818-2A-->G) or donor (c.1060+1G-->A, c.1845+1delG and c.2547+1G-->A) spice sites. These findings emphasise that care must be taken before reporting the presence or absence of a splice-site mutation in the LDLR gene for diagnostic purposes. The study also shows that relatively simple, quick and inexpensive RNA assays can evaluate putative splicing mutations that are not always predictable by available software, thereby reducing genetic misdiagnosis of patients with FH.
- In silico versus in vitro analysis of LDLR mutationsPublication . Alves, A.C.; Silva, S.; Patel, D.; Malhó, R.; Soutar, A.K.; Bourbon, M.The LDL receptor (LDLR) is a glycoprotein that mediates binding and internalization of cholesterol-rich lipoproteins from plasma. Mutations in the LDLR gene are the major cause of familial hypercholesterolaemia (FH), which results in impaired catabolism of circulating LDL. This common autosomal inherited metabolism disorder leads to premature atherosclerosis and increased risk of CHD. Many different mutations (currently more than 1300) have been identified in FH patients, but not all give rise to a defective LDLR.
- In vitro functional characterization of missense mutations in the LDLR genePublication . Silva, S.; Alves, A.C.; Patel, D.; Malhó, R.; Soutar, A.K.; Bourbon, M.Mutations in the LDL receptor gene are the major cause of familial hypercholesterolaemia (FH) but it has been previously shown that the simple finding of a variation in the coding sequence of the LDLR does not confirm that it is the actual cause of FH. The pathogenicity of five missense alterations in the LDLR gene coding sequence found in a previous epidemiologic study was investigated.
- A rare polymorphism in the low density lipoprotein (LDL) gene that affects mRNA splicingPublication . Bourbon, M.; Sun, X.M.; Soutar, A.K.Familial hypercholesterolaemia (FH) is usually caused by mutations in the low density lipoprotein (LDL) receptor gene (LDLR) that impair clearance of LDL from the circulation. The increased risk of premature coronary heart disease associated with FH can be reduced by dietary advice and treatment with lipid-lowering drug therapy, but it is important to identify affected individuals at an early stage. Several programmes for genetic diagnosis of FH that rely on identifying nucleotide substitutions in genomic DNA have been initiated, but the validity of these is dependent on distinguishing between a silent nucleotide variant and a mutation that affects LDL-receptor function. Here we describe a single nucleotide substitution in the coding region of exon 9 of LDLR that is an apparently silent polymorphism: CGG (Arg406) to AGG (Arg). Analysis of mRNA from the patient's cells showed that the mutation introduces a new splice site that is used to the exclusion of the natural splice site and causes a deletion of 31 bp from the mRNA, predicted to introduce premature termination four codons after R406. This finding emphasizes the caution needed in genetic diagnosis of FH based on genomic DNA sequence alone.