TaqMan Systems for Genotyping of Disease-Related Polymorphisms Present in the Gene Encoding Apolipoprotein E

Polymorphisms of the gene encoding apolipoprotein E have been implicated in the pathogenesis of peripheral and coronary artery disease and neurodegenerative disorders such as sporadic and late-onset familial forms of Alzheimer's disease. We have developed TaqMan assay systems for the single nucleotide polymorphisms -219G/T, located in the promoter of the apolipoprotein E gene, 113G/C, present in the transcriptional enhancer element of intron 1, 334T/C, determining Cys or Arg as amino acid residue 112 of mature apolipoprotein E, and 472C/T, determining Arg or Cys as residue 158. The accuracy of genotype determination with the TaqMan systems was demonstrated by analyses with restriction endonucleases. We determined the genotypes of the apolipoprotein E polymorphisms in 2349 study subjects. The genotypes were distributed as: -219GG= 27.3%, -219GT= 49.1%, and -219TT=23.6% (p=0.435); 113GG=41.3%, 113GC= 45.2%, and 113CC=13.5% (p=0.343); 334TT=73.4%, 334TC=24.7%, and 334CC= 1.9% (p=0.539); 472CC=86.3%, 472CT=12.8%, and 472TT= 0.9% (p=0.004) (Hardy-Weinberg equilibrium estimates are given in parentheses). The allele combinations which define the three major isoforms of apolipoprotein E, namely apoE2, apoE3, and apoE4, had the following allele frequencies: 334T/472T (epsilon 2; 112Cys/158Cys)=7.3%, 334T/472C (epsilon 3; 112Cys/158Arg)=78.4%, and 334C/472C (epsilon 4; 112Arg/158Arg)=14.2%, respectively. ApoE genotypes were distributed as: epsilon 2 epsilon 2=0.9%, epsilon 2 epsilon 3= 11.2%, epsilon 2 epsilon 4= 1.6%, epsilon 3 epsilon 3=61.3%, epsilon 3 epsilon 4=23.19 1 0, and epsilon 4 epsilon 4=1.9% (p=0.014). The TaqMan assays allow for fast and sensitive genotyping and are especially suitable for studies including large numbers of participants.