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Biomedical subjects

A E Retief

Publications and source records attributed to A E Retief.

At least 37 records · Page 2Linked to original sources
PubMed1990

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. A cytosine to guanine base substitution at nucleotide position 681 of the LDL receptor cDNA results in an amino acid change from aspartic acid to glutamic acid at residue 206 in the cysteine rich ligand binding domain of the LDL receptor. Since three previously mapped transport deficient alleles of the LDL receptor were also traced to cysteine rich repeats of the protein, these results suggest that the mutation is responsible for the receptor defective mutation predominantly found in Afrikaner FH homozygotes. The mutation gives rise to an additional DdeI restriction site in DNA of affected subjects and segregation of the mutation with the disease was confirmed in five large Afrikaner FH families. We predict that 65% of affected South African Afrikaners carry this particular base substitution. Amplification of genomic DNA, using the polymerase chain reaction method, and restriction enzyme analysis now permit accurate diagnosis of the mutation in subjects with FH.

Alleles↗
PubMed1989

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. DNA from a hetero-allelic FH homozygote from this South African group has been analysed through genomic cloning and sequencing. The DNA polymorphic site is caused by a single guanine to adenine transition within exon 8 of the LDL receptor gene and can be used in the determination of haplotype-associated defects.

Cloning, Molecular↗
PubMed1989

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. A second mutation, a guanine to adenine base substitution in exon 9, was identified in two homozygous FH individuals. Restriction enzyme analysis of PCR-amplified DNA from blood and tissue samples now permits accurate diagnosis of these mutations.

DNA Mutational Analysis↗
PubMed1989

Confirmation of a balanced chromosomal translocation using molecular techniques.

Investigation of a couple, who had produced three babies with cri du chat syndrome, showed initially that the mother had an apparent deletion of chromosome 5. It seemed likely that she had a balanced chromosomal translocation but it proved impossible to detect the second chromosome involved using routine cytogenetic methods. Molecular techniques using quantitative hybridization dosage studies were performed and these showed that the mother had a double dose of DNA in the suspected deleted area of chromosome 5. Further studies, using in situ hybridization techniques, revealed that the missing segment of chromosome 5 had translocated onto the short arms of a C group chromosome and further analysis of prometaphase chromosomes showed the presence of a balanced translocation, 46,XY,t(5;9)(5qter----5p14.1::9p22----9pter;9 qter----9p22::5p14.1----5pter). As a result of these findings, it was possible to offer prenatal diagnosis to the patient in future pregnancies, by detecting the presence of a balanced or unbalanced translocation in the fetus using molecular and cytogenetic techniques.

Adolescent↗
PubMed1989

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. Recombination events were not detected in any of the families studied and we thus conclude that the haplotypes associated with FH function as specific markers for the disease and will allow presymptomatic diagnosis in affected families.

Adolescent↗
PubMed1987

Haplotype associations of three DNA polymorphisms at the human low density lipoprotein receptor gene locus in familial hypercholesterolaemia.

The frequency and inheritance of three restriction fragment length polymorphisms (RFLPs) of the low density lipoprotein (LDL) receptor gene were investigated in 27 South African families with familial hypercholesterolaemia. Four haplotypes, defined by the enzymes PvuII, StuI, and NcoI, were found to segregate in this population. The frequency of the rare allele detected by NcoI was found to be 0.53 in 45 unrelated familial hypercholesterolaemic (FH) patients compared to 0.33 in 60 normal controls (p less than 0.005). In 71% of the families studied, a haplotype with common alleles for PvuII and StuI and the rare allele for NcoI cosegregated with the defective gene. In 20% of the families, a second haplotype with rare alleles for PvuII and StuI and common allele for NcoI segregated with FH. In these families the haplotypes unambiguously cosegregate with the disease and can therefore be used for early diagnosis of FH.

Adult↗