Apolipoprotein E phenotype determined by agarose gel electrofocusing and immunoblotting.

Polymorphism at the apolipoprotein E (ApoE) locus is an important factor in the development of remnant (Type III) hyperlipidemia and also influences the distribution of cholesterol concentrations in the population. The new method for ApoE phenotyping described here gives good results with simple apparatus. Serum (10 microL) is digested with sialidase (EC 3.2.1.18), delipidated, and redissolved in 6 mol/L urea. Electrofocusing is carried out in agarose, followed by immunoblotting with a monoclonal antibody to ApoE and an anti-immunoglobulin-peroxidase conjugate. Sialidase-catalyzed digestion effectively removes sialated forms of ApoE, which eases interpretation. This method can be used in nonspecialist laboratories and is particularly suited for assay of large numbers of samples.