Characterization of a novel variant of apolipoprotein E, E2 Fukuoka (Arg-224 → Gln) in a hyperlipidemic patient with xanthomatosis

Abstract

A new variant of apolipoprotein (apo) E, designated apo E2 Fukuoka, was identified in a 54-year-old Japanese woman who suffered from hyperlipoproteinemia (total cholesterol 29.7 mmol/l, triglyceride 12.0 mmol/l, when she was 48-year-old) with the presence of xanthoma in the palms, bones, and ocular fundi, and other sites. Foam-cell macrophages were observed in bone marrow specimens. Analysis of apo E phenotype showed the E3/E2 isoform on isoelectric focusing performed on plasma, but the E3/E3 isoform on restriction-fragment-length polymorphism of the apo E gene. This discrepancy indicated that the apo E had an amino-acid substitution outside of amino-acid residues at 112 and 158. Sequence analysis of the patient's DNA, which was amplified by PCR and subcloned, revealed a single substitution from arginine (CGG) to glutamine (CAG) at residue 224, thereby adding one negatively charged unit to apo E3. Recombinant apo E2 Fukuoka produced in COS-1 cells showed almost the same binding activity to the LDL receptor on human skin fibroblasts as compared with recombinant apo E3. Recombinant apo E2 Fukuoka showed the same heparin binding ability than recombinant apo E3. Findings indicated that apo E2 Fukuoka was not the primary cause of the hyperlipoproteinemia observed in this case.