Prenatal diagnosis of familial hypercholesterolemia: importance of DNA analysis in the high-risk South African population.

In this report on the outcome of the first prenatal diagnosis performed for familial hypercholesterolemia (FH) in a South African family, we aim to demonstrate the value of a population-directed screening strategy to identify FH patients in populations with an enrichment for certain low-density lipoprotein receptor (LDLR) gene mutations. Prenatal diagnosis was offered to an Afrikaner couple, both partners heterozygous for the FH mutation D206E, whose first child was diagnosed with heterozygous FH and the second with homozygous FH. Genomic DNA isolated from parental peripheral blood and subsequently amniotic fluid was amplified by the polymerase chain reaction (PCR) and subjected to mutation analysis.

Familial adenomatous polyposis coli in South Africa--molecular basis and diagnosis.

Objective: To determine the molecular basis and establish a routine molecular diagnostic service for familial adenomatous polyposis coli (FAP) families in South Africa.

Design: The coding region of the adenomatous polyposis coli (APC) gene in affected FAP kindreds was screened using heteroduplex analysis, single-strand conformation polymorphism analysis and the protein truncation test.

Setting: Department of Human Genetics, University of Stellenbosch, and the Cancer Research Campaign Laboratories, Department of Pathology, University of Edinburgh and Molecular Medicine Centre, Western General Hospital, Edinburgh, Scotland (academic visit of 6 months).

High prevalence of the Cys282Tyr HFE mutation facilitates an improved diagnostic service for hereditary haemochromatosis in South Africa.

Objective: The aim of the study was to investigate the molecular basis of hereditary haemochromatosis (HH) in South Africa in order to establish a reliable, cost-effective molecular diagnostic service for this potentially lethal disorder.

Design: DNA samples of patient and control groups were screened for two common haemochromatosis (HFE) gene mutations. The local frequencies of mutations C282Y and H63D were determined and the DNA results correlated with biochemical parameters.

CpG hotspot mutations at the LDL receptor locus are a frequent cause of familial hypercholesterolaemia among South African Indians.

Mutation analysis of genomic DNA samples obtained from seven unrelated South African Indians with familial hypercholesterolaemia (FH) revealed two novel and two recurrent missense mutations in the low density lipoprotein receptor (LDLR) gene. The novel mutations are transversions of C to G and A to T at nucleotide positions 1215 (N384K) and 2356 (S765C), respectively. The known mutations were detected in CpG dinucleotides at bases 661 and 682, respectively, in the mutation-rich exon 4 of the LDLR gene.

Two novel point mutations causing receptor-negative familial hypercholesterolemia in a South African Indian homozygote.

Two novel point mutations have been identified in the low density lipoprotein receptor (LDLR) gene of a South African Indian patient with a clinical diagnosis of homozygous familial hypercholesterolemia (FH). The patient is a compound heterozygote, whose paternally-inherited allele has a single base substitution of A to T at position + 1. This conversion of the initiation codon ATG (methionine) to TTG (leucine) would abolish initiation of translation at the normal site, and consequently the synthesis of any normal LDLR molecules.

Two novel frameshift mutations in the low density lipoprotein receptor gene generated by endogenous sequence-directed mechanisms.

DNA samples from 60 unrelated Belgian hypercholesterolemic patients were subjected to heteroduplex analysis of exon 4 of the low density lipoprotein receptor (LDLR) gene. Aberrant mobility bands were detected in 2 patients and the underlying mutations were characterized by DNA sequence analysis. Both mutations, a 19-bp insertion at codon 141 and a 23bp deletion at codon 168, produce premature stop codons in the highly conserved ligand binding domain of the mature LDLR.

FH Afrikaner-3 LDL receptor mutation results in defective LDL receptors and causes a mild form of familial hypercholesterolemia.

Three founder-related gene mutations (FH Afrikaner-1, -2, and -3) that affect the LDL receptor are responsible for 90% of the familial hypercholesterolemia (FH) in South African Afrikaners. Patients heterozygous for the FH Afrikaner-1 (FH1) mutation, which results in receptors having approximately 20% of normal receptor activity, have significantly lower plasma cholesterol levels and milder clinical symptoms than heterozygotes with the FH Afrikaner-2 mutation, which completely abolishes LDL receptor activity. In this study we re-created the FH3 mutation (Asp154-->Asn) in exon 4 by site-directed mutagenesis and analyzed the expression of the mutant receptors in Chinese hamster ovary cells.

Nonradioactive multiplex PCR screening strategy for the simultaneous detection of multiple low-density lipoprotein receptor gene mutations.

We have developed a rapid, nonradioactive screening test enabling the simultaneous analysis of three low-density lipoprotein receptor (LDLR) gene mutations (D154N, D206E, and V408M), which together account for familial hypercholesterolemia (FH) in approximately 90% of the South African Afrikaner population. The assay is designed so that FH patients, negative for these founder-related mutations (found in descendants of European settlers), subsequently can be screened for unknown mutations in the mutation-rich exon 4 of the LDLR gene. Our screening assay consists of two steps: (1) multiplex allele-specific PCR amplification of exons 4 and 9, and (2) simultaneous analysis of single- and double-strand conformational polymorphisms in exon 4 by vertical electrophoresis on low cross-linked polyacrylamide gels.

Recurrent LDL-receptor mutation causes familial hypercholesterolaemia in South African coloureds and Afrikaners.

Three low-density lipoprotein receptor (LDLR) gene mutations were previously shown to cause familial hypercholesterolaemia (FH) in up to 90% of affected Afrikaners. Association of each mutation with a single chromosomal background provided molecular genetic evidence that the proposed 'founder gene effect' was responsible for the high prevalence of FH among white Afrikaners. In this study we report the identification of the FH Afrikaner-2 (FH2) mutation, Val408 to Met, in the so-called coloured population of South Africa, a people of mixed ancestry, with rapid non-radioactive methods for mutation detection.

Familial defective apolipoprotein-B is rare in hypercholesterolaemic South African Afrikaners, coloureds and Indians.

The frequency of familial defective apolipoprotein B-100 (FDB) was assessed among hypercholesterolaemic Afrikaners, coloureds and Indians. Patients selected for screening did not carry any of the founder or common LDL-receptor mutations known to be associated with these groups. No FDB was detected and the mutation is therefore a rare cause of hypercholesterolaemia in these South African populations.

Screening for mutations in exon 4 of the LDL receptor gene: identification of a new deletion mutation.

DNA from 14 unrelated New Zealand familial hypercholesterolaemia (FH) heterozygotes, originating from the United Kingdom, was screened for mutations in exon 4 of the low density lipoprotein receptor (LDLR) gene. One patient was heterozygous for mutation D206E, which was initially identified in South Africa. The chromosomal background of this mutant allele was compatible with that described previously in Afrikaner and English patients, suggesting that this mutation originated in the United Kingdom.

Phenotypic expression and frequency of familial defective apolipoprotein B-100 in Belgian hypercholesterolemics.

DNA screening for apolipoprotein (apo) B mutations causing familial defective apolipoprotein B-100 (FDB) was performed in 87 hyperlipidemic Belgian individuals using heteroduplex analysis. Eighteen FDB heterozygotes from 5 unrelated families were identified. Three of the index cases reported an early family history of premature coronary heart disease (CHD).

Detection of two point mutations causing familial defective apolipoprotein B-100 by heteroduplex analysis.

Familial defective apolipoprotein B-100 (FDB) is a dominantly-inherited genetic disorder causing primary hypercholesterolemia and premature coronary heart disease. To date, only two mutations causing FDB have been identified. A rapid non-radioactive technique is described to detect both disease-related apolipoprotein B point mutations in polymerase chain reaction (PCR) products amplified from genomic DNA.

Report on a molecular diagnostic service for familial hypercholesterolemia in Afrikaners.

The development of DNA-based methods for the direct detection of specific low density lipoprotein receptor (LDLR) gene mutations enabled us to establish a molecular diagnostic service for familial hypercholesterolemia (FH). This specialised service is of particular relevance and can be applied in the Afrikaner population of South Africa, where a founder gene effect increased the prevalence of FH to about 5-10 times greater than that found in most other population groups. Three point mutations in the LDLR gene were shown to account for approximately 90% of all Afrikaner FH cases.

Phenotypic variation among familial hypercholesterolemics heterozygous for either one of two Afrikaner founder LDL receptor mutations.

Two common founder-related gene mutations that affect the low-density lipoprotein receptor (LDLR) are responsible for approximately 80% of familial hypercholesterolemia (FH) in South African Afrikaners. The FH Afrikaner-1 (FH1) mutation (Asp206-->Glu) in exon 4 results in defective receptors with approximately 20% of normal activity, whereas the FH Afrikaner-2 (FH2) mutation (Val408-->Met) in exon 9 completely abolishes LDLR activity (< 2% normal activity). We analyzed the contribution of these mutations and other factors on the variation of hypercholesterolemia and clinical features in Afrikaner FH heterozygotes.

Intrafamilial variability in the clinical expression of familial hypercholesterolemia: importance of risk factor determination for genetic counselling.

A specific mutation in the low-density lipoprotein receptor (LDLR) gene causes familial hypercholesterolemia (FH) in about 60% of Afrikaner FH heterozygotes. Molecular diagnosis of this so-called FH Afrikaner-1 mutation was performed in a family with the disease. One individual did not develop coronary heart disease (CHD) by age 84, despite having the FH Afrikaner-1 mutation, while his son who inherited the same gene, developed CHD before age 50 and had to undergo bypass surgery.

DNA screening of hyperlipidemic Afrikaners for familial hypercholesterolemia.

Three different point mutations of the low-density lipoprotein receptor (LDLR) gene are responsible for familial hypercholesterolemia (FH) in about 90% of Afrikaner patients. Screening of hyperlipidemic Afrikaner individuals for these founder-related mutations was performed to determine the distribution of the mutations in individuals with different lipid profiles, and to provide guidelines for screening of the mutations in hyperlipidemics. Rapid DNA methods, based on restriction enzyme analysis or allele-specific hybridisation of enzymatically-amplified genomic DNA, have been used to analyse the LDLR gene mutations in four groups of Afrikaner individuals.

Detection of a frequent polymorphism in exon 10 of the low-density lipoprotein receptor gene.

DNA sequencing of enzymatically-amplified exons of the low-density lipoprotein receptor gene from several individuals revealed a polymorphism in exon 10 of the gene. The codon for arginine 450 was converted from AGG to AGA in some alleles.

The molecular basis and diagnosis of familial hypercholesterolaemia in South African Afrikaners.

Three different point mutations were recently identified in South African familial hypercholesterolaemics. These mutations result in the modification of recognition sites of specific restriction endonucleases. This study describes rapid methods for presymptomatic detection of these defects based on restriction enzyme analysis or allele-specific hybridization of enzymatically amplified genomic DNA.

An exon 4 mutation identified in the majority of South African familial hypercholesterolaemics.

The prevalence of familial hypercholesterolaemia (FH) is significantly higher in the Afrikaans speaking population (Afrikaners) of South Africa than reported in most other populations. A founder gene effect has been proposed to explain the high FH frequency, implying that the same low density lipoprotein (LDL) receptor gene defect is present in the majority of affected Afrikaners. By using DNA amplification and sequence determination, we have detected a point mutation in DNA from two Afrikaner FH homozygotes.

The identification of two low-density lipoprotein receptor gene mutations in South African familial hypercholesterolaemia.

Two point mutations were discovered in the low-density lipoprotein genes of patients with familial hypercholesterolaemia (FH). Defective genes were cloned and/or amplified by the polymerase chain reaction (PCR) method and the DNA sequences determined. A guanine to adenine base transition in exon 4 was found to be the molecular defect in 20% of cases of FH in the Afrikaner population.

Molecular characterisation of a low-frequency mutation in exon 8 of the human low-density lipoprotein receptor gene.

The prevalence of familial hypercholesterolaemia (FH), an autosomal dominant disease characterised by raised low-density lipoprotein (LDL) cholesterol levels, is at least five times higher in the white Afrikaner population than in most other population groups in the world. A founder gene effect has been suggested to explain this abnormally high frequency. Detection of a polymorphic Stu I site in the 5' region of the LDL receptor gene and association of both restriction fragment length polymorphism alleles with FH in Afrikaners, indicated the existence of at least two founder members for the disease in this population.

Haplotypes identified by 10 DNA restriction fragment length polymorphisms at the human low density lipoprotein receptor gene locus.

Ten useful two allele restriction fragment length polymorphisms of the low density lipoprotein receptor gene were used for haplotype analysis in 45 unrelated familial hypercholesterolaemic (FH) patients, 60 normal controls, and 32 FH homozygotes, all of whom were white Afrikaners. Pedigree analysis in 27 informative heterozygous FH and 23 normal families has shown the segregation of at least 17 haplotypes in the normal population (111 chromosomes) compared to a predominant association of two of these haplotypes with the disease in the FH subjects. This association was further confirmed in 32 FH homozygotes, indicating at least two 'founder' members for the disease in the Afrikaner population.