Simple Sequence-specific-Primer-PCR Method To Identify the Three Main Apolipoprotein E Haplotypes

Apolipoprotein E (ApoE) is involved in the binding, internalization, and catabolism of lipoprotein particles. ApoE is secreted by macrophages and hepatocytes and serves as a ligand for the LDL (Apo B/E) receptor and on hepatic tissues for the specific ApoE type 1 and 2 receptors for triglyceride-rich remnants (1)(2). The gene coding for ApoE is located on chromosome 19q13.32 and contains several polymorphic loci. The three common isoforms of ApoE, termed E2, E3, and E4, are defined by two single-nucleotide polymorphisms (SNPs) at positions 2059(T/C) and 2197(C/T) of the gene, which are located in the codons that code for amino acids 112 and 158 of the mature protein. The presence of a T allele at position 2059 (2059-T) of the gene defines a cysteine at position 112 (Cys112), whereas 2059-C defines an arginine for the same position (Arg112). Similarly, 2197-C on the gene defines an arginine at position 158 (Arg158), whereas 2197-T codes for cysteine for the same position (Cys158). ApoE3 (Cys112/Arg158) is the most common of the three isoforms found. The ApoE2 isoform Cys112/1Cys158 is associated with remnant hyperlipidemia because this isoform has a lower affinity for ApoE receptors. The ApoE4 (Arg112/Arg158) isoform is associated with increased hepatic synthesis of VLDL and is a risk factor for Alzheimer disease and other neurologic diseases. Other rare isoforms are also found and are associated with mixed hyperlipidemia (1).Several methods have been used for genotyping the three major ApoE isoforms. The problems inherent in phenotyping methods have led to the gradual adoption of genotyping methods for determination of ApoE isoforms in most laboratories (3). By far the commonest method has been PCR amplification followed by restriction fragment length polymorphism (RFLP) analysis. Although many variations of …