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.
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