Detection of apoB-100 R3500Q mutation by competitive allele-specific polymerase chain reaction

The apolipoprotein B-100 mutation R3500Q is one of the most common inherited defects causing abnormality of the lipid metabolism. We describe a one-step, single-tube PCR technique for detection of the mutation based on competition between allele-specific primers. Three oligonucleotides are used: two allele-specific primers differing in their 3' nucleotide (for the wild-type and the mutant allele) together with a common primer, resulting in simultaneous amplification of both alleles. This provided internal control of successful amplification and is expected to result in increased specificity. The allele-specific primers differ also in length, allowing us to distinguish both alleles by their size in a single electrophoretic run. For optimization of the protocol, DNAs genotyped before by oligonucleotide ligation assay were used. The individual genotypes obtained by CAS-PCR coincided fully with the ones from a referent OLA test: seven heterozygous individuals were found, 4 of them among 150 unrelated hypercholesterolemic individuals studied and other three in the pedigrees of heterozygous carriers. On the overall 160 genotypes were determined, neither false-positive (0 out of 153 non-carriers) nor false-negative (0 out of 7 carriers) results were obtained. No homozygous mutant genotypes were identified in this sample.