Mutations in the apolipoprotein (apo) B-100 receptor-binding region: Detection of apo B-100 (Arg(3500)--> Trp) associated with two new haplotypes andevidence that apo B-100 (Glu(3405)-> Gln) diminishes receptor-mediated uptake of LDL

Background: Ligand-defective apolipoprotein (apo) B-100 is a major cause of hypercholesterolemia. For many years, apo B-100 (Arg(3500) --> Gln) has be en the only mutation known to cause ligand-defective apo B-100. Methods: Using temperature gradient gel electrophoresis, we screened 297 un related individuals with LDL-cholesterol >1.55 g/L and triglycerides <2.0 g /L for sequence variants of the putative LDL receptor-binding domain of apo B-100. Results: We found apo B-100 (Arg(3500) --> Gln) in 21 individuals (7.1%). W hen extrapolated to the general population, this corresponds to the highest prevalence of apo B-100 (Arg3500 --> Gln) reported to date. Furthermore,,v e identified three unrelated carriers (1%) of a silent substitution (CTG -- > CTA) affecting the codon for leucine(3350), four carriers (1.3%) of apo B -100 (Glu(3405) --> Gln), and two subjects (0.7%) with apo B-100 (Arg(3500) --> Trp). apo B-100 (Arg(3500) --> Trp) was assigned to two different, pre viously unknown haplotypes. The binding, uptake, and degradation of apo B-1 00 (Arg(3500) --> Trp) was lower than that of normal LDL, but higher than,v ith apo B-100 (Arg(3500) --> Gln), implying that the substitution of Trp(35 00) for Arg may cause less severe reduction of binding than the substitutio n of Gln. LDL from individuals heterozygous for apo B-100 (Glu(3405) --> Gl n) bound to LDL receptors at the same rate as normal LDL, but was taken up and degraded at significantly reduced rates, suggesting that domains of apo B-100 involved in binding and uptake do not completely overlap. Conclusions: In Germany, apo B-100 (Arg(3500) --> Gln) may be more frequent than previously assumed. Both apo B-100 (Arg(3500) --> Trp) and apo B-100 (Glu3405 --> Gln) may contribute to the phenotype of ligand-defective LDL. These variants will be missed if screening is confined to apo B-100 (Arg(35 00) --> Gln) only. (C) 1999 American Association for Clinical Chemistry.