Rapid Identification of Apolipoprotein E Genotypes by Multiplex Amplification Refractory Mutation System PCR and Capillary Gel Electrophoresis

Apolipoprotein E(Apo E) genotyping on its own is neither sufficiently sensitive nor specific enough for use as a predictive diagnostic test for Alzheimer disease (AD) (1). Nevertheless, it is still of diagnostic value in the classification of type III hyperlipidemia (2). Furthermore, there exists a great research need and interest for Apo E genotyping in conjunction with other data relating to genetic polymorphisms. Several independent studies have now established that the inheritance of one or more Apo ε4 alleles increases an individual’s risk of developing atherosclerosis and AD (3)(4). Conversely, the inheritance of one or more ε2 alleles confers protection against AD (5) and is associated with lower lipid concentrations (6). Thus, a rapid and simple genotyping test is needed for any laboratory that takes part in clinical research related to Apo E. Apo E is a polymorphic protein consisting of a single polypeptide chain, 299 amino acids long. In plasma, it exists mainly in a nonglycosylated form. The three major isoforms of the protein are Apo E2, Apo E3, and Apo E4. These differ from each other by cysteine-arginine interchanges at amino acid residues 112 and 158. The biosynthesis of each protein isoform is under the control of three independent codominant alleles, ε2, ε3, and ε4, located at a single Apo E gene locus on chromosome 19q13. Depending on the inheritance of any two alleles, six common Apo E genotypes are possible, three homozygotes (ε2ε2, ε3ε3, and ε4ε4) and three heterozygotes (ε2ε3, ε3ε4, and ε2ε4) (7).