Detection of apolipoprotein E variants by an oligonucleotide "melting" procedure.

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 epsilon 3 allele but not the common epsilon 2 allele, the other recognizing the epsilon 2 allele but not the epsilon 3 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.