Simultaneous detection of multiple familial hypercholesterolemia mutations facilitates an improved diagnostic service in South african patients at high risk of cardiovascular disease.

AIM: DNA testing can provide a definitive diagnosis of familial hypercholesterolemia (FH), even in the absence of the clinical characteristics of this inherited cardiovascular disease (CVD) subtype. Our aim was to design a rapid diagnostic assay capable of simultaneously analyzing seven point mutations in the low-density lipoprotein receptor (LDLR) gene, which occur at high frequency in South African FH patients. METHODS: The test is based on multiplex DNA amplification and hybridization to membrane strips presenting a parallel array of immobilized allele-specific oligonucleotide probes. RESULTS: A reverse-hybridization assay for genotyping LDLR point mutations D154N, D200G, D206E, C356Y, G361V, V408M, and P664L was set-up and validated using pretyped human DNA samples, as well as recombinant plasmid clones containing mutant alleles. The procedure is rapid (6 hours) and may be automated to a large extent. CONCLUSIONS: The new FH strip-assay forms an important part of the comprehensive cardiovascular genetic screen offered routinely to high-risk population groups in South Africa. A genetic approach based on FH testing in conjunction with other 'genetic' CVD risk factors is feasible and justified, since the spectrum of disease-related mutations have been defined to a large extent in the genetically distinct population groups of South Africa. Knowledge of a significantly increased CVD risk due to the presence of gene variations, which can be targeted for risk reduction by the avoidance of relevant environmental risk factors and the appropriate treatment, provides a powerful message to motivate people into implementing preventative measures based on their genetic profile.

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 MboII (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 (10.5%) 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.