Detection of apolipoprotein E variants by an oligonucleotide 'melting' procedure

Abstract

An oligonucleotide 'melting' procedure was developed whereby we can monitor for a sequence heterogeneity in the gene for apolipoprotein E production. Two oligonucleotides were synthesized, one recognizing the common ε3 allele but nor the common ε2 allele, the other recognizing the ε2 allele but not the ε3 allele. Samples from 15 subjects with different apolipoprotein E phenotypes as classified by isoelectric focusing were analyzed by this method for the presence of an Arg → Cys substitution in position 158 of the apolipoprotein E amino acid sequence. In 14 of these subjects the genotype determined by oligonucleotide melting agreed with the phenotype identified by isoelectric focusing. In one patient, however, whose phenotype was E2/2 by isoelectric focusing, the DNA hybridized with both oligonucleotides. We conclude that this patient has a mutation in one of his alleles for apolipoprotein E that differs from the frequently seen Arg → Cys change. The apolipoprotein E gene may thus be more heterogeneous than previously anticipated.