PHENOTYPIC-EXPRESSION AND FREQUENCY OF FAMILIAL DEFECTIVE APOLIPOPROTEIN B-100 IN BELGIAN HYPERCHOLESTEROLEMICS

DNA screening for apolipoprotein (ape) 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). The frequency of the apo B-3500 mutation was 8% in Belgians with type IIa hyperlipidemia, indicating that the prevalence of FDB may be as high as 1 in 250 in the general Belgian population. Plasma lipid levels of the patients identified in the present study are similar to those previously reported for FDB heterozygotes. We compared these data with results obtained in a genotype/phenotype correlation study of heterozygous familial hypercholesterolemia (FH) in the Afrikaner population of South Africa. Plasma cholesterol levels in FDB heterozygotes were similar to those reported for FH heterozygotes with defective receptors (Asp(206) --> Glu, approximate to 20% normal receptor activity), but significantly lower than in FH heterozygotes with a mutant protein which virtually lacks receptor activity (Val(408) --> Met, < 2% normal receptor activity). FDB appears to be a significant genetic cause of hypercholesterolemia in Belgium.