Comparative analysis of familial hypercholestrerolaemia in different populations

Thesis (Ph.D.) -- University of Stellenbosch, 1999.ENGLISH SUMMARY: Familial hypercholesterolaemia (FH) and familial defective apolipoprotein B-IOO (FDB) are relatively common disorders of lipid and lipoprotein metabolism caused by mutations in the low density lipoprotein receptor (LDLR) and apolipoprotein B (apo B) genes, respectively. DNA analyses at these loci were performed in 132 molecularlyuncharacterised South African, 11 Costa Rican and 13 New Zealand subjects with clinical features of heterozygous FH. Mutation R3500Q causing FDB was identified in a relatively large proportion (~30%) of the New Zealand patients. LDLR gene defects were identified in 4 Costa Rican and 6 New Zealand FH patients. Sixty-five different LDLR gene mutations were identified in South African hypercholesterolaemics, revealing ten founder-type mutations. Haplotype analysis at the LDLR and apo B loci excluded the likelihood that mutations in these two genes underlie the FH phenotype in one of the New Zealand families. The apparently autosomal dominant hypercholesterolaemia (ADH) in this family could also not be linked to a newly identified gene locus, designated FH3. Analysis of the New Zealand study cohort, although small, demonstrated both mutational and locus heterogeneity in ADH. Analysis was also extended to include subjects from the various ethnic groups within South Africa. The high prevalence of FH in Afrikaners of European descent is in striking contrast to the reported virtual absence of this lipid disorder in the Black South African population. In addition to three previously-described Afrikaner founder mutations (D154N, D206E and V408M), four minor founder mutations, D200G, S285L, C356Y and G361V, were identified in 12 Afrikaner families. Surprisingly, a 6-bp deletion in exon 2 of the LDLR gene was detected at a relatively high frequency (28%) in Black FH patients. This finding, as well as clinical correlations performed in the patients, suggests that the expression of FH mutations in the Black population may be altered due to interaction with other genetic and/or environmental factors, therefore leading to underdiagnosis of the disease. Common LDLR gene mutations have also been described in South African Indians (P664L) and Jews (del 197), most likely as a consequence of multiple introductions of defective genes into these relatively isolated communities. Caucasoid admixture was recognised as a major factor contributing to the FH phenotype in the indigenous South African population of mixed ancestry from the Western Cape, where six founder-type mutations account for the disease in 22% of cases. The high prevalence of specific LDLR gene mutations in different population groups facilitates an improved diagnostic service for FH in South Africa.AFRIKAANSE OPSOMMING: Familiele hipercholesterolemie (FH) en familiele defektiewe apolipoprotelen B-I00 (FDB) is relatief algemene afwykings in lipied en lipoprotelen metabolisme wat onderskeidelik veroorsaak word deur mutasies in die lae digtheids lipoprotelen reseptor (LDLR) en apolipoproteleri B-I00 (apo B) gene. Molekulere DNS analise van hierdie lokusse is uitgevoer in 132 Suid Afrikaanse, 11 Costa Rikaanse en 13 New Zealandse pasiente waar die geen mutasies onderliggend, aan die kliniese beeld van heterosigotiese FH onbekend was. Mutasie R3500Q wat FDB veroorsaak was in 'n relatief groot aantal van die New Zealandse pasiente (~30%) teenwoordig. LDLR geen defekte is in 4 Costa Rikaanse en 6 New Zealandse FH pasiente geldentifiseer. Vyf en sestig verskillende LDLR geen mutasies is aangetoon in die Suid Afrikaanse populasie waarvan tien stigtergeen mutasies is. Haplotipe analise van die LDLR en apo B lokusse het die moontlikheid uitgesluit dat mutasies in hierdie twee gene verantwoordelik is vir die FH fenotipe in een van die New Zealandse families. Die waarskynlik outosomaal dominante hipercholesterolemie (ODH) in hierdie familie kon ook nie toegeskryf word aan 'n nuwe geidentifiseerde geen lokus genaamd FH3 nie. Analise van die New Zealandse studie paneel het dus beide mutasie en lokus heterogeniteit in ODH gedemonstreer. Analise was uitgebrei deur die toevoeging van individue van verskeie etniese groepe van Suid-Afrika. Die hoe voorkoms van FH in Afrikaners van Europese afkoms is , in opvallende kontras met die voorheen vermeende feitlike afwesigheid van hierdie lipied afwyking in die Swart Suid-Afrikaanse populasie. Afgesien van drie bekende Afrikaner stigter mutasies (D154N, D206E en V408M), is nog vier relatief algemene mutasies, D200G, S285L, C356Y en G361V, ge'identifiseer in 12 Afrikaner families. 'n Onverwagse bevinding was die opsporing van 'n 6-bp delesie in ekson 2 van die LDLR geen teen 'n relatief hoe frekwensie (28%) in Swart FH pasiente. Hierdie bevinding, sowel as kliniese korrelasies wat in hierdie groep pasiente uitgevoer is, impliseer dat FH moontlik ondergediagnoseer word in die Swart populasie weens interaksie van defektiewe LDLR gene met ander genetiese en/of omgewingsfaktore. Algemene LDLR geen mutasies is ook beskryf in Suid Afrikaanse Indiers (P664 L) en J ode (del 197), heel waarskynlik as 'n gevolg van veelvuldige oordrag van defektiewe gene in hierdie relatief geisoleerde gemeenskappe. Kaukasier vermenging is herken as 'n belangrike faktor onderliggend aan die FH fenotipe in die inheemse W es-Kaapse kleurling populasie van Suid-Afrika, waar ses stigter-tipe mutasies verantwoordelik is vir die siekte in 22% van' gevalle. Die hoe voorkoms van spesifieke LDLR geen mutasies in verskillende populasie groepe maak populasie-gerigte DNA dililgnose van FH moontlik in Suid Afrika

Clinical versus molecular diagnosis of heterozygous familial hypercholesterolaemia in the diverse South African population

Objective. Familial hypercholesterolaemia (FH) is a common genetic disease characterised by strikingly elevated. plasma cholesterol concentration, which can lead to premature coronary death if left untreated. In this study DNA diagnosis of FH, which allows detection before onset of clinical symptoms, was evaluated against biochemical parameters routinely used to identify subjects with FH.Design. A population-based strategy was used to identify low-density lipoprotein receptor (LDLR) gene defects in South Africans with clinical signs of FH, followed by a family-based DNA screening approach for presymptomatic diagnosis of FH.Results. DNA screening of 790 at-risk relatives for the FHrelated mutations identified in 379 index cases, allowed accurate disease diagnosis in an additional 338 relatives and exclusion of the relevant mutation in 452 individuals. The sensitivity and speeifidty of the diagnosis, based on total cholesterol values measured in family members of FH heterozygous index cases with one of the three founderrelated mutations, D154N, D206E and V408M, were 89.3% and 81.9%, respectively.Conclusion. The predominance of 10 LDLR gene mutations in the local population justifies population-directed D A diagnosis of FH in South Africa on a routine basis, particularly since expression of the defective gene measured in biochemical tests does not allow accurate diagnosis of FH in all cases. D A testing provides a definitive tool for family tracing aimed at pre-clinical diagnosis and preventive treatment of FH

Clinical versus molecular diagnosis of heterozygous familial hypercholesterolaemia in the diverse South African population

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Analysis of two mutations in the MTHFR gene associated with mild hyperhomocysteinaemia – heterogeneous distribution in the South African population

Objective, The frequencies of mutations 677C→T and 1298A→C in the methylenetetrahydrofolate reductase (MTHFR) gene, previously shown to be associated with decreased enzyme activity that may lead to hyperhomocysteinaemia and consequently increased risk of cardiovascular disease (CVD), were determined in the South African population.Methods, Hinfi (677C→T) and MbolI (1298A→C) restriction enzyme analyses were performed on amplified DNA samples of 76 white, 73 coloured and 60 black subjects.Results, The mutant alleles of mutations 677C→T and 1298A..-+C were more common in the white (allele frequencies 0.36 and 0.37, respectively) than in the black population (0.04 and 0.09), while intermediate frequencies were detected in the coloured population (0,18 and 0.30); Homozygosity for mutation 677C → T was not detected in the black cohort, while this genotype was detected in 1 coloured (1.4%) and 8 white (105%) subjects, In the black population, 5% of the 60 subjects analysed were homozygous for mutation 1298A→C, compared with approximately 12% in both the white and coloured populations,Conclusions. Since hyperhomocysteinaemia is a risk factor for premature CVD, the heterogeneous distribution of the 677C→T and 1298A→C mutations across ethnic groups may partly explain ethnic differences in heart disease risk through decreased enzyme activity and hence increased homocysteine levels

Die molekulere analise van mutante cf-gene vir mutasie-identifikasie

Proefskrif (M.Sc.(Geneeskundige Wetenskappe)) -- Universiteit van Stellenbosch, 1994.Een kopie mikrofiche.Full text to be digitised and attached to bibliographic record

LDLR Database (second edition): new additions to the database and the software, and results of the first molecular analysis

Mutations in the LDL receptor gene (LDLR) cause familial hypercholesterolemia (FH), a common autosomal dominant disorder. The LDLR database is a computerized tool that has been developed to provide tools to analyse the numerous mutations that have been identified in the LDLR gene. The second version of the LDLRdatabase contains 140 new entries and the software has been modified to accommodate four new routines. The analysis of the updated data (350 mutations) gives the following informations: (i) 63% of the mutations are missense, and only 20% occur in CpG dinucleotides; (ii) although the mutations are widely distributed throughout the gene, there is an excess of mutations in exons 4 and 9, and a deficit in exons 13 and 15; (iii) the analysis of the distribution of mutations located within the ligand-binding domain shows that 74% of the mutations in this domain affect a conserved amino-acid, and that they are mostly confined in the C-terminal region of the repeats. Conversely, the same..