Improved phenotyping of apolipoprotein E: application to population frequency distribution.

A simple procedure for phenotyping apolipoprotein (apo) E directly from plasma has been developed for use in the lipid clinic laboratory. In this new method, 10 microL of serum or plasma is pretreated with neuraminidase (EC 3.2.1.18), which removes the sialic acid residues from apo E and eliminates additional bands, thereby ensuring correct phenotype assignment. After a rapid delipidation step, the samples are focused in vertical polyacrylamide mini-slab gels and immunoblotted with a polyclonal goat anti-apo E antibody, followed by a Protein G-peroxidase conjugate. The accuracy of this method was confirmed by comparison with the established procedure of phenotyping by isoelectric focusing of delipidated very-low-density lipoprotein. In addition, sera from 203 subjects from Vancouver, selected without conscious bias, were used to determine the local distribution of the apo E alleles. We estimate that the relative frequencies of apo E alleles epsilon 2, epsilon 3, and epsilon 4 in this population are 0.086, 0.761, and 0.153, respectively. The speed and convenience of using minigels make this procedure ideal for clinical laboratory applications and large population studies.