CHARACTERIZATION OF 5 NEW MUTANTS IN THE CARBOXYL-TERMINAL DOMAIN OF HUMAN APOLIPOPROTEIN-E - NO COSEGREGATION WITH SEVERE HYPERLIPIDEMIA

Assessment of the apolipoprotein E (apoE) phenotype by isoelectric foc using of both hyperlipidemic and normolipidemic individuals identified five new variants. All mutations were confined to the downstream part of the APOE gene by using denaturing gradient gel electrophoresis (DG GE). Sequence analysis revealed five new mutations causing unique amin o acid substitutions in the carboxyl-terminal part of the protein cont aining the putative lipid-binding domain. Three hyperlipoproteinemic p robands were carriers of the APOE2(Val236-->Glu) allele, the APOE*3(C ys112-->Arg; Arg251-->Gly) allele, or the APOE1(Arg158-->Cys; Leu252- ->Glu) allele. DGGE of the region encoding the receptor-binding domain was useful for haplotyping the mutations at codons 112 and 158. Famil y studies failed to demonstrate cosegregation between the new mutation s and severe hyperlipoproteinemia, although a number of carriers for t he APOE3(Cys112-->Arg; Arg251-->Gly) allele and the APOE*1(Arg158-->C ys; Leu252-->Glu) allele expressed hypertriglyceridemia and/or hyperch olesterolemia. Two other mutant alleles, APOE4- (Cys112-->Arg; Arg274 -->His) and APOE4+(Ser296-->Arg), were found in normolipidemic proban ds. The lack of cosegregation of these new mutations with severe hyper lipoproteinemia suggests that these mutations do not exert a dominant effect on the functioning of apoE.